How to Validate a Custom LiPo Battery Sample Before Mass Production

Receiving a custom LiPo battery sample is an important project milestone, but a battery that fits the enclosure, powers the device, and completes one charging cycle is not automatically ready for mass production.

A custom battery can fail later because of issues that are difficult to detect during a quick bench test:

• The finished pack exceeds the dimensional tolerance

• The connector fits but has the wrong polarity or pinout

• Peak current causes excessive voltage drop

• The protection circuit interrupts normal startup

• The battery becomes too warm inside the final enclosure

• Standby current shortens storage or operating life

• Capacity varies between samples

• The charger and battery use incompatible voltage limits

• Wires, insulation, or the PCM move during vibration or assembly

• Prototype construction differs from the intended production process

• A design change is introduced after sample approval

Sample validation should therefore answer two different questions:

1. Does the battery design work correctly in the intended device?

2. Can the supplier reproduce that approved design consistently in mass production?

This guide explains how to create a validation plan, inspect a custom LiPo battery sample, test its electrical and mechanical performance, evaluate production readiness, document approval, and avoid common mistakes before placing a mass-production order.

Key Takeaways

• Approve a battery against written requirements, not general impressions.

• Define pass/fail criteria before testing begins.

• Confirm whether the sample is an engineering sample or a production-intent sample.

• Validate the finished battery pack, not only the pouch cell.

• Record the cell, PCM or BMS, connector, wire, firmware, label, and construction revision.

• Check maximum dimensions and tolerances rather than nominal dimensions alone.

• Verify connector part number, pinout, polarity, cable length, and cable exit direction.

• Measure capacity under controlled conditions and runtime in the actual device.

• Test continuous current, startup current, peak current, and repeating pulse loads separately.

• Evaluate voltage drop and temperature rise throughout the complete current path.

• Confirm charger compatibility and protection behavior under normal and fault conditions.

• Test the battery inside the final enclosure with production-intent device hardware and software.

• Do not use one unusually good sample to represent future production consistency.

• Safety, transport, and market-access testing do not replace application validation.

• Keep approved reference samples and a signed specification package.

• Complete a controlled pilot build before releasing a high-volume order.

• Require notification and revalidation for material, process, firmware, or supplier changes.

What Does Custom LiPo Battery Sample Validation Mean?

Custom LiPo battery sample validation is the structured process of comparing a proposed battery design with the electrical, mechanical, thermal, functional, reliability, and compliance requirements of the final product.

It is more comprehensive than checking whether the battery can turn on the device.

A complete validation process may cover:

• Battery identity and revision

• Cell model and chemistry

• Nominal and maximum dimensions

• Capacity and stored energy

• Charge and discharge behavior

• Continuous and peak current

• Voltage drop

• Internal resistance

• Runtime

• Temperature rise

• PCM or BMS functions

• NTC response

• Connector and wiring

• Device communication

• Mechanical fit

• Cable routing

• Vibration and drop performance

• Cycle life

• Storage behavior

• Compliance documentation

• Production consistency

• Change control

The final scope depends on the device, battery design, operating environment, target market, risk level, and expected production volume.

A small promotional device and a medical monitoring product should not use identical validation plans, even if both use a single-cell 3.7 V LiPo battery.

Understand Which Type of Sample You Received

Not every sample represents the same stage of development. Before beginning validation, ask the supplier how the battery was built and what decisions have already been frozen.

A sample should not receive final approval if it contains temporary components that will be replaced during production.

Ask the supplier to identify any differences involving:

• Cell model

• Cell manufacturing location

• Electrode or electrolyte system

• PCM or BMS

• MOSFETs

• Fuse

• NTC thermistor

• Connector

• Terminals

• Wire supplier and gauge

• Nickel interconnects

• Insulation

• Adhesive

• Pouch orientation

• Label

• Firmware

• Welding or soldering process

• Pack assembly process

• Testing process

If differences remain, approval should be conditional or limited to the functions that the sample can genuinely represent.

Begin With a Written Battery Specification

Testing without a written specification often produces an unclear result. One team may consider the sample acceptable because it powers the device, while another rejects it because runtime is shorter than expected.

Before testing, establish a controlled specification that defines the approved requirements.

Electrical Requirements

Record:

• Cell chemistry

• Series and parallel configuration

• Nominal voltage

• Maximum charge voltage

• Rated capacity

• Minimum acceptable capacity

• Nominal energy

• Standard charging current

• Maximum charging current

• Typical discharge current

• Maximum continuous discharge current

• Peak current

• Peak duration

• Repeating pulse profile

• Device cutoff voltage

• Battery protection thresholds

• Internal-resistance target

• Standby-current target

• Required runtime

• Operating temperature

• Charging temperature

• Storage temperature

• Cycle-life target

Mechanical Requirements

Record:

• Maximum finished-pack thickness

• Maximum width

• Maximum length

• Dimensional tolerances

• Weight limit

• Cell and PCM position

• Cable exit direction

• Wire gauge

• Cable length

• Connector location

• Connector orientation

• Permitted bend radius

• Insulation requirements

• Label position

• Adhesive or mounting method

• Expansion allowance

• Enclosure clearance

• Restricted or keep-out areas

Connection Requirements

Record:

• Connector manufacturer

• Connector series

• Exact part number

• Mating connector

• Terminal part number

• Pin count

• Pinout

• Polarity

• Wire colors

• NTC lead

• Communication wires

• Balance leads

• Shielding or strain relief, if required

Functional Requirements

Record:

• Overcharge protection

• Over-discharge protection

• Charge over-current protection

• Discharge over-current protection

• Short-circuit protection

• Temperature sensing

• Cell balancing

• Fuel gauging

• State-of-charge reporting

• State-of-health reporting

• Cycle count

• Authentication

• Fault logging

• Communication protocol

• Sleep and wake-up behavior

• Shipping mode

• Fault-recovery behavior

Product and Compliance Requirements

Record:

• Application type

• Target markets

• Required safety standards

• Transportation requirements

• Environmental restrictions

• Required reports and certificates

• Traceability requirements

• Label and marking requirements

• Quality agreement

• Warranty expectations

• Change-notification requirements

ZERNE’s custom Li-polymer battery solutions can incorporate cell selection, capacity, PCM or BMS functions, temperature sensing, wires, connectors, insulation, and pack structure around the requirements of an OEM device.

Convert the Specification Into a Validation Matrix

A requirement is easier to approve when it is connected to a defined test, acceptance limit, sample quantity, and responsible party.

A validation matrix may use the following structure:

The numbers in the acceptance column should come from the approved cell specification, pack specification, device requirements, component ratings, risk analysis, and applicable standards.

Do not copy generic limits from another battery project without confirming that they apply to the new design.

Decide How Many Samples to Test

There is no single correct sample quantity for every custom battery project.

The required quantity depends on:

• Product risk

• Battery complexity

• Number of test groups

• Destructive versus non-destructive testing

• Expected production volume

• Cell and component maturity

• Supplier experience

• Regulatory requirements

• Confidence required in variability

• Whether samples are engineering-built or production-built

One or two samples may identify an obvious compatibility problem, but they cannot demonstrate production consistency.

A larger validation set allows the team to examine:

• Average performance

• Minimum and maximum results

• Variation between units

• Early failures

• Differences between test groups

• Repeatability of dimensions and assembly

• Performance after environmental exposure

• Production-lot consistency

The sample plan should also include:

• Units for electrical testing

• Units for mechanical and environmental testing

• Units for cycle or aging tests

• Units reserved for investigation

• Unused reference units

• Production-intent units from the pilot build

Do not repeatedly use the same sample for incompatible tests unless the test plan specifically allows it. Previous cycling, high-temperature exposure, mechanical stress, or protection testing can affect later results.

Step 1: Verify Sample Identity and Traceability

Before measuring performance, confirm exactly what has been delivered.

Each sample or sample lot should be traceable to:

• Supplier name

• Customer project

• Battery part number

• Battery revision

• Cell model

• Cell lot or date code

• PCM or BMS revision

• Firmware revision, if applicable

• Connector and wire specification

• Assembly date

• Sample-build quantity

• Manufacturing location

• Inspection record

• Test report

• Drawing revision

• Specification revision

Photograph each sample before testing. Include:

• Front and rear surfaces

• Label

• Connector

• Wire routing

• Cable exit

• PCM area

• Sealing edges

• Any visible date or lot code

Assign each unit a unique test ID. Results such as capacity, resistance, dimensions, runtime, and temperature should be connected to that ID rather than reported only as a group average.

Why Traceability Matters

If a sample fails, the team must be able to determine whether the cause is related to:

• One defective unit

• One component lot

• One assembly process

• One design revision

• One test method

• The entire battery concept

Without traceability, investigation becomes guesswork and corrective actions may address the wrong cause.

Step 2: Review the Documents Before Testing

Request the documents needed to understand and control the proposed design.

Depending on the project, these may include:

• Battery specification

• Cell specification

• Mechanical drawing

• Connector drawing

• Pinout diagram

• PCM or BMS specification

• Protection-threshold table

• NTC specification

• Communication specification

• Charging requirements

• Material or component list

• Sample inspection report

• Capacity and internal-resistance data

• Safety data sheet

• Transport test summary

• Applicable compliance reports

• Label drawing

• Packaging specification

• Reliability-test plan

• Process flow

• Quality-control plan

• Change history

Check that the model numbers and revisions agree across all documents.

Common document conflicts include:

• A drawing showing a different wire length from the sample

• A label using an old capacity value

• A PCM report listing different thresholds from the pack specification

• A connector drawing with a reversed pinout

• A cell report that does not match the installed cell model

• A test report for a similar battery rather than the proposed battery

• A certificate that covers the cell but not the finished pack configuration

Do not assume that a certificate or report applies merely because the voltage and capacity look similar. Confirm the covered model or product family and the permitted construction differences.

Step 3: Perform Visual and Workmanship Inspection

Inspect the samples before applying electrical stress.

Look for:

• Pouch dents

• Creases

• Swelling

• Scratches

• Corrosion

• Contamination

• Electrolyte leakage

• Damaged sealing edges

• Exposed conductive material

• Sharp folds

• Loose tape

• Misaligned insulation

• Uneven label placement

• Poor strain relief

• Damaged wire insulation

• Loose connector terminals

• Incorrect wire colors

• Poor soldering or welding

• Excess adhesive

• Foreign material

• Unprotected PCM components

• Inconsistent cable routing

The inspection criteria should reflect the agreed construction. A visual difference is not automatically a defect, but unexplained variation between supposedly identical samples should be investigated.

Inspect the Pouch Carefully

The aluminum-laminated pouch should not be punctured, sharply bent, compressed by a hard component, or exposed to an edge that could damage it during assembly or use.

Pay particular attention to:

• The transition between the cell body and top seal

• Folded tabs

• PCM placement

• Nickel-strip edges

• Connector terminals

• Adhesive locations

• Enclosure ribs or screws near the pouch

A battery may look acceptable outside the device but experience damaging pressure after the enclosure is closed.

Step 4: Measure the Finished Battery Dimensions

Measure the complete battery assembly rather than relying on the pouch-cell model number.

Record:

• Maximum thickness

• Maximum width

• Maximum length

• PCM or BMS projection

• Seal and tab area

• Cable length

• Connector dimensions

• Cable exit position

• Weight

The drawing should define:

• Measurement reference points

• Nominal dimensions

• Maximum dimensions

• Tolerances

• State of charge during measurement

• Temperature during measurement

• Whether insulation and label are included

• Whether wires and connectors are included in the envelope

A LiPo model number may indicate the approximate size of the pouch cell, but it does not necessarily represent the completed battery. Protection components, tape, wiring, sealing edges, and production tolerances can increase the required space.

Check Fit in the Actual Device

Install multiple samples in production-intent enclosures and confirm:

• The battery can be inserted without force

• The pouch is not pinched or sharply bent

• The enclosure closes normally

• Screws do not contact or compress the battery

• The cable follows the intended route

• The connector can be inserted and removed

• The wire does not cross a sharp edge

• The battery does not move excessively

• Adhesive and foam do not create excessive pressure

• Other components cannot rub against the pouch

• Appropriate service-life expansion space remains available

A battery should not be approved merely because the smallest sample fits. Use the maximum permitted battery dimensions and the minimum permitted enclosure space in the tolerance evaluation.

Step 5: Confirm Connector, Pinout, and Polarity

Connector errors can damage the battery, charger, or device immediately.

Before connecting the sample:

1. Confirm the connector manufacturer and exact part number.

2. Compare it with the mating connector.

3. Check terminal and housing compatibility.

4. Verify the number of pins.

5. Compare the physical pin positions with the drawing.

6. Measure polarity using appropriate equipment.

7. Confirm NTC and communication leads.

8. Check wire gauge and cable length.

9. Verify strain relief and terminal retention.

10. Record the result for every sample.

Do not rely on:

• Wire color alone

• Connector appearance

• A previous supplier’s pin convention

• Positive and negative markings on an unverified drawing

Two visually identical two-pin connectors can use opposite polarity.

For multi-wire batteries, verify the complete pinout, including:

• Pack positive

• Pack negative

• NTC

• Identification resistor

• Data

• Clock

• Enable

• Balance connections

If the battery communicates with the device, confirm electrical levels, timing, address, data format, error handling, and wake-up behavior.

Step 6: Record Incoming Electrical Condition

Before cycling, record the sample’s as-received condition.

Relevant measurements may include:

• Open-circuit voltage

• State of charge

• Pack voltage

• Individual series-group voltages

• Internal resistance

• Battery weight

• Communication status

• Fault flags

• Shipping-mode status

• Date received

• Time since manufacture

Large variation in incoming voltage or resistance may indicate inconsistent conditioning, storage, self-discharge, cell matching, or assembly.

However, measurements should be interpreted carefully. Internal-resistance results can change with:

• Test method

• Test frequency

• Contact resistance

• State of charge

• Cell temperature

• Rest time

• Equipment accuracy

Use the same validated measurement method for comparisons.

Step 7: Verify Capacity and Stored Energy

Rated capacity should be checked under controlled conditions defined in the battery specification.

A basic capacity test normally involves:

1. Charging the battery using the approved charging profile

2. Allowing the specified rest period

3. Discharging at the defined current

4. Stopping at the specified cutoff condition

5. Recording delivered ampere-hours and watt-hours

6. Recording voltage and temperature throughout the test

The exact current, voltage, temperature, rest time, and termination conditions affect the result.

Rated Capacity vs Device Runtime

Capacity and runtime are related, but they are not interchangeable.

A battery can meet its laboratory capacity rating and still provide inadequate device runtime because of:

• High device current

• Pulse loads

• Voltage conversion losses

• Early device shutdown

• Protection-circuit voltage drop

• Low operating temperature

• Inaccurate state-of-charge estimation

• High standby current

• Connector or wire resistance

Validate both:

• Controlled battery capacity

• Runtime under a defined real-device use profile

Compare Every Sample

Do not report only the best result or the group average.

Record:

• Individual capacity

• Minimum result

• Maximum result

• Average

• Variation

• Any abnormal charge or discharge curve

• Temperature during testing

• Test equipment and calibration status

If one sample performs substantially worse than the others, investigate it even if the average remains acceptable.

Step 8: Test the Real Device Load Profile

A simple resistive load may not reproduce how the final product uses the battery.

The validation plan should represent:

• Sleep current

• Standby current

• Typical operating current

• Maximum continuous current

• Startup current

• Motor-stall current

• Radio-transmission pulses

• Display activation

• Heater inrush

• Processor or wireless peaks

• Repeating duty cycles

• Charging while operating, if applicable

Continuous-Current Test

Confirm that the battery can sustain the required current without:

• Excessive voltage drop

• Excessive temperature rise

• PCM or BMS interruption

• Connector heating

• Wire heating

• Unstable device operation

Peak-Current Test

Record:

• Peak magnitude

• Peak duration

• Repetition rate

• Battery state of charge

• Battery temperature

• Minimum pack voltage

• Protection response

• Device response

A battery may support one short pulse but fail when the pulse repeats frequently or occurs near the end of discharge.

Startup Test

Startup is often more demanding than steady operation.

Test startup under relevant worst-case conditions, such as:

• Low state of charge

• Minimum operating temperature

• Maximum device load

• Aged-battery condition

• Repeated restart

• Motor or pump startup

• Wireless transmission during startup

If the protection circuit trips during a legitimate device load, simply increasing its current rating may not solve the problem. Cell capability, voltage drop, wiring, connector resistance, MOSFET losses, detection delay, and device behavior should be evaluated together.

Step 9: Validate Charging Compatibility

The battery, charger, protection circuit, and device firmware must function as one charging system.

Confirm:

• Charging method

• Maximum charge voltage

• Charging current

• Pre-charge behavior

• Constant-current stage

• Constant-voltage stage

• Charge termination

• Recharge or restart behavior

• Charging time

• Battery temperature

• Connector temperature

• PCM or BMS temperature

• Device status indication

• Charging while the device is operating

• Response to an interrupted charge

• Response after protection cutoff

Test With the Production-Intent Charger

A laboratory power supply can help diagnose the battery, but it does not replace testing with the final charger and device.

Differences in:

• Voltage accuracy

• Current control

• Termination current

• Cable resistance

• Communication

• Temperature sensing

• Timer behavior

• Firmware

• USB power negotiation

can change charging performance.

Confirm Temperature Control

If the battery includes an NTC thermistor, verify:

• NTC resistance value

• Resistance tolerance

• Reference temperature

• Beta value or resistance curve

• Physical sensor location

• Connector pin

• Device or charger interpretation

• Charge and discharge limits

• Fault behavior for an open or shorted sensor

An NTC only senses temperature. The device, charger, PCM, or BMS must interpret the signal and take the required action.

Step 10: Measure Voltage Drop and Temperature Rise

Voltage and temperature should be measured throughout the actual current path.

Potential heat sources include:

• Cell

• Tabs

• Welds

• Nickel interconnects

• MOSFETs

• Current-sense resistor

• Fuse

• Wires

• Connector terminals

• PCB traces

• Device contacts

A battery that passes an open-bench test may become significantly warmer inside a sealed enclosure.

Use Realistic Test Conditions

Consider:

• Maximum intended load

• Maximum charging current

• Low state of charge

• Highest intended ambient temperature

• Minimum airflow

• Final enclosure

• Final foam and adhesive

• Production cable routing

• Simultaneous charging and device operation

• Repeated peak loads

Acceptance limits should be based on:

• Cell specification

• Component ratings

• Insulation ratings

• Connector and wire limits

• Device requirements

• User-contact requirements

• Applicable safety standards

• Expected service life

Do not approve the design using only the maximum measured surface temperature of the enclosure. Internal battery and component temperatures may be higher.

Step 11: Verify PCM or BMS Functions

The required tests depend on whether the battery uses a basic PCM or a more advanced BMS.

Relevant functions may include:

• Overcharge detection

• Over-discharge detection

• Charge over-current detection

• Discharge over-current detection

• Short-circuit response

• Temperature monitoring

• Cell-voltage monitoring

• Cell balancing

• Current measurement

• State-of-charge estimation

• State-of-health estimation

• Cycle counting

• Fault logging

• Authentication

• Communication

• Sleep mode

• Shutdown mode

• Shipping mode

• Wake-up behavior

• Fault recovery

Evaluate Threshold and Recovery Behavior

For each protection function, confirm:

• Detection threshold

• Detection delay

• Cutoff behavior

• Current consumption after cutoff

• Release or recovery condition

• Interaction with the charger

• Interaction with device firmware

• Behavior after repeated faults

Protection tests must be conducted with controlled equipment and appropriate safety measures. Hazardous or destructive testing should be performed only by qualified personnel or laboratories using an approved procedure.

Test Normal Loads Near Protection Boundaries

The protection circuit should respond to faults without interrupting valid device behavior.

Potential conflicts include:

• Startup current mistaken for a short circuit

• Motor stall triggering repeated cutoff and recovery

• Device cutoff occurring below the PCM threshold

• Charger restart loops after over-discharge

• BMS sleep mode preventing the device from waking

• Cell balancing extending charging time

• State-of-charge data becoming inaccurate under pulse loads

A circuit can pass its own component-level test and still be unsuitable for the device.

Step 12: Validate Runtime and User-Visible Battery Behavior

Run the battery in the final device using a documented operating profile.

The test should define:

• Starting state of charge

• Charging procedure

• Ambient temperature

• Device hardware revision

• Firmware revision

• Screen or radio activity

• Load duty cycle

• Sleep periods

• Endpoint condition

• Number of repeated runs

Record:

• Total runtime

• Voltage curve

• Reported battery percentage

• Device shutdown point

• Protection cutoff point

• Temperature

• Reset or brownout events

• Remaining capacity at shutdown

• Recharge behavior after shutdown

Check Battery-Percentage Accuracy

If the device displays state of charge, compare the reported value with actual battery behavior.

Look for:

• Sudden percentage drops

• Long periods at 100%

• Early shutdown with capacity remaining

• Device operation after 0%

• Inconsistent readings after restart

• Incorrect readings at low temperature

• Loss of calibration after battery replacement

Fuel-gauge performance may require calibration using the final cell, load profile, cutoff voltage, and firmware settings.

Step 13: Test Standby, Sleep, and Storage Behavior

Low-power products can lose more energy through standby consumption than expected.

Measure current in:

• Normal operation

• Idle mode

• Sleep mode

• Device shutdown

• Battery shipping mode

• Protection cutoff

• Charger disconnected state

• Long-term storage state

Include consumption from:

• PCM or BMS

• Fuel gauge

• Communication circuit

• NTC network

• Device electronics

• Leakage paths

• Charger input

Estimate storage or standby duration using realistic usable capacity and current consumption. Do not divide nominal capacity by one measured current without considering:

• Self-discharge

• BMS or PCM consumption

• Temperature

• Aging

• Minimum device voltage

• Protection cutoff

• Capacity tolerance

• Shipping state of charge

Long-term storage testing may also monitor:

• Open-circuit voltage

• Capacity retention

• Recovery after storage

• Swelling

• Internal resistance

• Communication status

• Excessive self-discharge

Step 14: Evaluate Mechanical and Environmental Performance

The necessary tests should reflect the final application rather than a generic checklist.

Possible evaluations include:

• Device assembly and disassembly

• Cable pull or retention

• Connector insertion and removal

• Vibration

• Mechanical shock

• Product drop

• Compression from the enclosure

• Thermal cycling

• High-temperature operation

• Low-temperature operation

• High-temperature storage

• Low-temperature storage

• Humidity exposure

• Altitude or low-pressure conditions

• Dust or moisture protection at device level

• Repeated button, motor, or radio operation

• Transportation packaging

After exposure, inspect and retest:

• Appearance

• Dimensions

• Open-circuit voltage

• Capacity

• Internal resistance

• Insulation

• Wiring

• Connector retention

• Protection functions

• Device operation

• Leakage or swelling

Mechanical testing should represent how the battery is mounted inside the product. Testing an unsupported battery outside the enclosure may not reproduce actual stresses.

Step 15: Evaluate Cycle Life and Aging

A new sample can meet capacity and power requirements but degrade too quickly for the intended product.

A cycle-life plan should define:

• Charging voltage

• Charging current

• Charge termination

• Discharge current

• Discharge cutoff

• Rest periods

• Temperature

• Device or laboratory load

• Measurement intervals

• End-of-life criterion

Track:

• Remaining capacity

• Energy

• Internal resistance

• Voltage drop

• Temperature rise

• Swelling

• Runtime

• Protection behavior

• Connector and wire condition

Consider Application-Specific Aging

Battery aging may accelerate when the device:

• Remains fully charged for long periods

• Operates at high temperature

• Uses frequent high-current pulses

• Repeatedly reaches deep discharge

• Charges while operating

• Has limited heat dissipation

• Spends long periods in storage

• Uses a high maximum charge voltage

A short accelerated test can support comparison, but it should not be treated automatically as an exact prediction of real-world service life. The relationship between test conditions and field use must be justified.

Step 16: Separate Product Validation From Compliance Testing

Device-level validation, battery safety evaluation, transport testing, and market certification serve different purposes.

A battery that works correctly in the device is not automatically compliant. Likewise, a battery with compliance documentation is not automatically compatible with the device.

Depending on the battery, product, destination, and distribution method, the project may need to evaluate requirements associated with:

• Lithium battery transportation

• Portable battery safety

• Cell or pack safety

• Product-level electrical safety

• Electromagnetic compatibility

• Environmental restrictions

• Recycling or labeling

• Air, sea, road, or rail shipment

UN 38.3 Is Not a Device Performance Test

UN 38.3 addresses the transport testing of lithium cells and batteries. It does not confirm:

• Device runtime

• Enclosure fit

• Charger compatibility

• Battery-percentage accuracy

• Cable routing

• Application temperature

• Peak-load capability

• Product drop performance

• Long-term cycle life

It also applies to a defined cell or battery design type. Changes to cells, construction, components, or configuration should be reviewed to determine whether existing reports remain applicable or additional testing is needed.

Confirm the Scope of Every Report

For each document, verify:

• Manufacturer

• Model number

• Cell or battery designation

• Physical description

• Voltage and capacity

• Series and parallel configuration

• Test report number

• Test date

• Applicable standard edition

• Test laboratory

• Pass/fail result

• Covered construction

• Permitted model family

• Differences from the proposed sample

Do not approve a custom pack based only on a report for its internal cell unless the project requirements allow that report to cover the relevant purpose.

Step 17: Compare Sample Results With Manufacturing Capability

A good prototype does not prove that the design can be manufactured consistently.

Before mass production, discuss:

• Critical dimensions

• Component tolerances

• Cell matching

• Welding parameters

• Soldering controls

• PCM programming

• Firmware loading

• Connector and wire verification

• Insulation placement

• Adhesive quantity

• Label control

• In-process testing

• Final inspection

• Traceability

• Equipment calibration

• Defect handling

• Rework limits

• Lot-release criteria

ZERNE’s Li-polymer battery quality control system describes controls including process monitoring, structural inspection, environmental control, cell tracking, and final performance verification. Sample approval should connect these manufacturing controls with the critical characteristics identified during validation.

Define Critical-to-Quality Characteristics

Characteristics that materially affect safety, compatibility, or performance should receive clear production controls.

Examples include:

• Cell model and lot

• Pack polarity

• Maximum finished thickness

• Connector part number

• Wire length

• Weld integrity

• Protection thresholds

• Firmware version

• Capacity

• Internal resistance

• Open-circuit voltage

• NTC value

• Communication

• Insulation

• Label accuracy

The control method, inspection frequency, equipment, acceptance limit, and record-retention requirement should be documented.

Step 18: Complete a Pilot Production Run

A pilot run uses the intended manufacturing process to determine whether the approved design can be reproduced.

It can reveal problems that hand-built samples do not show, including:

• Dimensional variation

• PCM-position variation

• Inconsistent wire length

• Connector polarity errors

• Weak welds

• Insulation misalignment

• Label mistakes

• Firmware-loading errors

• Cell-lot variation

• Test-station limits

• Packaging damage

What to Review During the Pilot Run

Review:

• Incoming component records

• Actual bill of materials

• Work instructions

• Process parameters

• In-process inspection

• Final-test data

• Yield

• Rework

• Defect types

• Dimensional distribution

• Capacity distribution

• Resistance distribution

• Traceability

• Packaging

• Shipment condition

Select units across the pilot lot rather than taking only the first units produced.

Repeat Critical Device Tests

Production-intent units should repeat the tests most important to the application, such as:

• Mechanical fit

• Connector and polarity

• Charging

• Runtime

• Peak load

• Temperature

• Communication

• Protection behavior

• Assembly

• Product operation

Pilot approval provides stronger evidence than relying entirely on engineering samples.

Create and Preserve a Golden Sample

A golden sample is an approved physical reference that represents the accepted battery construction and workmanship.

It may help confirm:

• Dimensions

• Cable routing

• Connector orientation

• Label position

• Insulation

• PCM location

• Overall appearance

However, a golden sample should not replace controlled documents. Physical units can age, become damaged, or fail to reveal internal design details.

The approved reference package should include:

• Golden sample

• Signed battery specification

• Approved drawing

• Approved bill of materials or controlled component list

• Connector and pinout drawing

• PCM or BMS specification

• Firmware revision

• Test plan

• Validation report

• Pilot-run report

• Compliance documents

• Packaging specification

• Change-control agreement

The supplier and customer should each retain an identified reference sample where practical.

How to Handle a Failed Sample

A failed test should lead to a structured investigation, not an undocumented sample replacement.

Record:

• Sample ID

• Test method

• Test condition

• Equipment

• Failure time

• Measured data

• Photographs

• Device revision

• Battery revision

• Environmental conditions

• Previous tests performed on the sample

Then determine whether the failure is related to:

• Requirement definition

• Battery design

• Cell capability

• Protection settings

• Connector or wire

• Device hardware

• Device firmware

• Charger

• Enclosure

• Test method

• Measurement equipment

• Manufacturing defect

• Sample damage

• Component variation

Require Corrective Evidence

A revised sample should be accompanied by:

• Root-cause analysis

• Corrective action

• Updated revision

• Description of changes

• Affected documents

• Retest plan

• Evidence that the change does not create a new problem

Do not test revised samples under an old part number or revision. Otherwise, failed and corrected designs become difficult to distinguish.

Retest Affected and Connected Functions

If a connector changes, retest more than physical engagement. Also consider:

• Polarity

• Contact resistance

• Temperature rise

• Cable routing

• Retention

• Device assembly

If the PCM changes, reconsider:

• Voltage drop

• Current capability

• Protection thresholds

• Sleep current

• Charging

• Device shutdown

• Temperature

• Compliance documentation

A change can correct one failure while affecting several other requirements.

Freeze the Approved Design Before Mass Production

Once validation is complete, freeze the approved configuration.

The controlled design should identify:

• Cell manufacturer and model

• Permitted cell alternatives

• Cell specifications

• PCM or BMS part number

• Protection settings

• MOSFET and fuse requirements

• Firmware

• NTC

• Connector

• Terminal

• Wire

• Cable length

• Insulation

• Adhesive

• Label

• Dimensions

• Assembly process

• Test limits

• Packaging

Avoid approval language such as “same or equivalent” unless equivalence has been defined and a formal approval process exists.

Establish Change Control

The supplier should notify the customer before making changes that may affect fit, function, performance, safety, reliability, compliance, or appearance.

Potential notification items include:

• Cell model or supplier

• Cell manufacturing location

• Electrode or electrolyte system

• Capacity rating

• PCM or BMS

• MOSFET

• Fuse

• Firmware

• Connector

• Terminal

• Wire

• NTC

• Nickel or busbar

• Insulation

• Adhesive

• Label material

• Dimensions

• Welding process

• Assembly process

• Production location

• Test method

• Packaging

The agreement should define whether a change requires:

• Document review

• New samples

• Partial revalidation

• Full revalidation

• New compliance testing

• Customer approval before implementation

Sample Approval Report Template

A clear approval report may contain the following sections.

1. Project Information

• Customer

• Product

• Device model

• Battery part number

• Battery revision

• Supplier

• Test dates

• Test location

• Responsible reviewers

2. Sample Information

• Sample quantity

• Sample IDs

• Cell model

• Cell lot

• PCM or BMS revision

• Firmware revision

• Assembly date

• Sample type

• Production location

3. Referenced Documents

• Battery specification

• Mechanical drawing

• Cell specification

• Protection specification

• Connector drawing

• Device specification

• Test plan

• Compliance documents

4. Test Equipment

• Equipment name

• Model

• Asset number

• Calibration status

• Accuracy or measurement capability

5. Test Results

For every test, record:

• Requirement

• Method

• Conditions

• Acceptance criterion

• Individual results

• Pass/fail conclusion

• Notes

• Supporting files

6. Deviations

Record:

• Deviation description

• Reason

• Technical assessment

• Temporary or permanent status

• Required corrective action

• Approval authority

7. Final Decision

Use a clear status such as:

• Approved

• Approved with documented conditions

• Rejected

• Additional testing required

• Approved for pilot production only

• Approved for mass production

Avoid ambiguous conclusions such as “basically acceptable” or “should be fine.”

Common Sample-Validation Mistakes

Final Mass-Production Approval Checklist

Requirements and Documents

• Battery specification approved

• Cell specification approved

• Mechanical drawing approved

• Connector and pinout approved

• PCM or BMS specification approved

• Charging requirements approved

• Label approved

• Packaging specification approved

• Required compliance documents reviewed

• Revisions consistent across all documents

Sample Identity

• Production-intent construction confirmed

• Sample IDs recorded

• Cell model and lot recorded

• PCM or BMS revision recorded

• Firmware recorded

• Components match the intended bill of materials

• Manufacturing location confirmed

Mechanical Validation

• Maximum dimensions pass

• Weight passes

• PCM placement passes

• Cable length passes

• Cable exit passes

• Connector orientation passes

• Device assembly passes

• Pouch is not pinched or damaged

• Expansion clearance is adequate

• Vibration or drop requirements pass

Electrical Validation

• Open-circuit voltage passes

• Capacity passes

• Energy passes

• Internal resistance passes

• Continuous current passes

• Peak current passes

• Startup current passes

• Voltage drop passes

• Runtime passes

• Standby current passes

• Charging behavior passes

Thermal Validation

• Cell temperature passes

• PCM or BMS temperature passes

• Connector temperature passes

• Wire temperature passes

• Enclosed-device temperature passes

• Worst-case operating condition passes

• Charging temperature passes

Protection and Communication

• Overcharge response verified

• Over-discharge response verified

• Over-current response verified

• Short-circuit response verified

• Temperature sensing verified

• NTC value and location verified

• Recovery behavior verified

• Sleep and wake-up verified

• State-of-charge behavior verified

• Communication verified

• Authentication verified, if required

Reliability and Production

• Cycle or aging requirement passes

• Storage requirement passes

• Environmental requirement passes

• Pilot production completed

• Production data reviewed

• Critical characteristics controlled

• Golden sample retained

• Validation report signed

• Change-control process agreed

• Corrective actions closed

• Mass-production release approved

Conclusion

A custom LiPo battery sample should not be approved simply because it fits the enclosure and powers the device.

Reliable approval begins with a controlled specification and measurable acceptance criteria. The finished battery should then be evaluated for identity, dimensions, connector and polarity, capacity, charging, runtime, continuous and peak current, voltage drop, temperature, protection functions, communication, mechanical integration, storage, and aging.

The most meaningful tests use the final device, charger, enclosure, firmware, cable routing, and operating profile. Supplier bench testing and customer device testing serve different purposes, and both may be necessary.

The sample must also represent the intended production design. A hand-built engineering unit cannot demonstrate that dimensions, welds, wiring, protection settings, and performance will remain consistent during mass production. A controlled pilot build, approved documentation, retained reference samples, and formal change control help connect successful sample testing with repeatable supply.

The goal is not to prove that one battery can work once. It is to confirm that the specified battery works safely and consistently in the intended product—and that the same approved design can be reproduced throughout production.

Frequently Asked Questions

What should I test on a custom LiPo battery sample?

At minimum, verify the battery’s identity, finished dimensions, connector, polarity, voltage, capacity, charging behavior, continuous and peak current, runtime, temperature rise, protection functions, and mechanical fit in the final device. The complete scope should reflect the application and target market.

Is one custom battery sample enough for approval?

Usually not. One sample can identify basic compatibility problems but cannot demonstrate unit-to-unit variation, reliability, or production consistency. The required quantity should be defined according to project risk, test scope, battery complexity, and regulatory requirements.

What is a production-intent battery sample?

A production-intent sample uses the cell, protection circuit, connector, wire, insulation, firmware, construction, and manufacturing process intended for mass production. Temporary or substitute components should be disclosed and resolved before final approval.

Should I test the bare cell or the finished battery pack?

Validate the finished battery assembly that will be installed in the product. A bare-cell test does not represent the voltage drop, dimensions, protection behavior, connector, wiring, insulation, or temperature of the completed battery.

How do I verify the capacity of a LiPo battery sample?

Use a controlled charge-discharge test with defined charging voltage, current, termination, rest time, discharge current, cutoff voltage, and temperature. Record individual results in both ampere-hours and watt-hours where appropriate.

Is rated capacity the same as device runtime?

No. Runtime also depends on device current, conversion efficiency, pulse loads, battery voltage, operating temperature, wiring losses, protection-circuit resistance, and the device’s shutdown threshold.

Why should the battery be tested inside the final enclosure?

The enclosure affects heat dissipation, battery compression, cable routing, airflow, connector position, and device assembly. A battery that performs correctly on an open bench may become too warm or experience mechanical stress inside the product.

How should peak current be tested?

Use a load profile that reproduces the magnitude, duration, and repetition rate of the actual device peak. Test at relevant temperatures and states of charge while recording minimum voltage, temperature, protection response, and device behavior.

What is the difference between an engineering sample and a golden sample?

An engineering sample is used during development and may still change. A golden sample is an approved physical reference representing the accepted production construction and workmanship. It should be supported by controlled drawings and specifications.

Does UN 38.3 approval mean the sample is ready for mass production?

No. UN 38.3 addresses lithium-cell and battery transport testing. It does not verify device fit, runtime, charger compatibility, peak-load performance, temperature inside the enclosure, or production consistency.

Can I use a certification report from the internal cell for the custom pack?

Not automatically. Confirm whether the report covers the finished battery configuration and intended purpose. Changes in series configuration, protection, wiring, enclosure, or other construction details may affect applicable requirements.

What should happen if a battery sample fails?

Document the failed unit, test condition, measured data, and battery revision. Determine the root cause, implement a controlled corrective action, issue a new revision where necessary, and repeat the affected tests. Connected functions should also be reviewed.

What is a pilot production run?

A pilot run produces a limited quantity using the intended components, equipment, work instructions, inspection methods, and manufacturing process. It helps confirm repeatability before a high-volume order is released.

Should the lowest test result or average result determine approval?

Both are important. An average can show overall performance, but minimum results and variation reveal whether individual units meet the requirement consistently. Acceptance rules should be defined before testing.

What changes should require customer notification?

Changes to the cell, PCM or BMS, firmware, connector, wire, NTC, fuse, insulation, dimensions, assembly process, production location, test method, or packaging may require notification and revalidation, depending on their effect on the approved product.

What information should I send to a LiPo battery manufacturer before sampling?

Provide the battery space, voltage, capacity, continuous and peak load, charging method, runtime target, connector, polarity, wire length, protection functions, operating temperature, device type, target market, compliance requirements, and expected order volume. Device drawings and load-profile data are especially useful.

When is a custom LiPo battery ready for mass production?

It is ready when production-intent samples meet the approved specification, critical device-level and reliability tests pass, required compliance documents have been reviewed, pilot production confirms repeatability, failures are closed, and the design and change-control process are formally approved.