LiPo Battery Connectors Explained: Main Lead, Balance Lead, JST, Molex, and Custom Options

A lithium polymer battery connector may look like a small component, but it directly affects power delivery, charging compatibility, assembly efficiency, and product reliability.

Choosing a connector only by appearance can create serious problems. Two connectors may have similar white housings but different pitches, terminal structures, locking features, current ratings, or pin arrangements. Even connectors from the same manufacturer may belong to entirely different series.

For OEM battery projects, the connector specification should define more than “JST,” “Molex,” or “two-pin plug.” It should identify the exact connector series, part number, wire size, cable length, polarity, pinout, mating component, and electrical load.

This guide explains the main types of LiPo battery leads, how JST and Molex connector families differ, and what to specify when ordering a standard or custom battery pack.

Key Takeaways

• The main lead normally carries the battery’s charge and discharge current.

• A balance lead monitors the voltage of individual series-connected cell groups.

• A conventional multi-cell balance connector usually has one more wire than the number of series groups.

• A 1S LiPo battery normally does not need a separate balance lead.

• “JST connector” and “Molex connector” are incomplete descriptions because both companies offer many connector families.

• Connector current capability depends on the exact series, terminal, wire size, number of circuits, temperature, and operating conditions.

• Pitch, circuit count, polarity, and pinout must be confirmed independently.

• A connector that physically mates is not automatically electrically compatible.

• Wire gauge and cable length affect voltage drop, heating, and available power.

• The mating connector on the device, PCB, charger, or test fixture should be confirmed before battery production.

• Any connector or harness change should be validated through samples before mass production.

Why LiPo Battery Connector Selection Matters

The connector forms the electrical and mechanical interface between the battery and the device. If that interface is poorly specified, even a correctly designed battery can perform unreliably.

A connector influences:

• Maximum continuous and peak current

• Voltage drop between the battery and device

• Heat generation at terminals and crimp points

• Available space inside the enclosure

• Resistance to vibration and accidental disconnection

• Assembly direction and cable routing

• Charging and balancing compatibility

• Serviceability and battery replacement

• Protection against reversed polarity

• Production and maintenance efficiency

The battery’s current requirement should be calculated before selecting the main connector. If the application has motors, heaters, pumps, wireless transmitters, or other high-load components, both steady current and short peak current must be considered.

The relationship between battery capacity, discharge rate, and current is explained in more detail in what the C rating of a Li-polymer battery means. The connector and wires must support the device’s actual current demand rather than simply match the battery capacity.

Main Lead vs Balance Lead

A LiPo battery pack may have one or several external leads. Each lead has a different purpose.

Some battery designs combine power, temperature sensing, communication, and identification connections in one multi-pin housing. The functions must therefore be verified from the wiring diagram rather than inferred from the number of wires.

What Is a LiPo Battery Main Lead?

The main lead is the primary electrical path between the battery pack and the load. In a conventional design, it consists of:

• One positive power wire

• One negative power wire

• A two-circuit connector or two individual terminals

The main lead may also be used for charging, depending on the battery and charger architecture.

What Determines the Main Lead Size?

The main lead should be selected according to:

• Maximum continuous current

• Peak current and peak duration

• Permitted voltage drop

• Wire length

• Ambient temperature

• Available airflow

• Connector contact resistance

• Number of current-carrying contacts

• Duty cycle

• Device safety margin

A connector’s published maximum current should not automatically be used as the design current. Manufacturer ratings are established under specified test conditions and may depend on the terminal, wire gauge, number of loaded circuits, and temperature.

Long or undersized wires add resistance. The resulting voltage drop can be estimated with:

Voltage drop = Current × Resistance

Heat generated in the connection increases according to:

Power loss = Current² × Resistance

This is why a connection that works during a low-current bench test may become hot when the device reaches its maximum operating load.

Can a Small JST Connector Be Used as a Main Connector?

Yes, in an appropriately low-current application.

Small single-cell LiPo batteries used in sensors, wearables, GPS trackers, Bluetooth products, and compact medical devices often use two-circuit wire-to-board connectors as their main connection. JST PH and compact Molex families are common examples.

However, a small connector should not be selected only because it fits inside the enclosure. Its electrical rating, wire range, terminal temperature rise, retention, and mating-cycle requirements must also match the application.

Higher-current products may need:

• A larger wire-to-board power connector

• A locking wire-to-wire connector

• Multiple contacts assigned to each power path

• A dedicated high-current two-pole connector

• Ring terminals, tabs, or another custom termination

• A combined connector designed specifically for the device

What Is a LiPo Battery Balance Lead?

A balance lead provides access to the electrical junctions between series-connected cell groups.

During charging, a balance charger or BMS can use these connections to measure the voltage of each series group. This helps prevent one group from reaching an excessive voltage while another remains undercharged.

For a conventional externally balanced pack:

The general relationship is:

Balance-lead circuits = Number of series groups + 1

For example, a 3S pack has three series-connected voltage groups. Its conventional balance lead normally includes the pack-negative reference and one connection for each successive series node, producing four wires in total.

Does a 2S2P Battery Need Three or Five Balance Wires?

A conventional 2S2P pack normally has three balance connections because balancing is based on the two series groups, not the total number of individual cells.

Cells connected in parallel form one voltage group. The balance system monitors the voltage of each series group.

Does a 1S LiPo Battery Need a Balance Lead?

Usually not.

A 1S pack contains only one series group, so there are no multiple series voltages to balance against each other. It commonly uses only a positive and negative main lead.

A third wire on a 1S battery may instead be used for:

• NTC temperature sensing

• Battery identification

• State monitoring

• Communication

• Charger control

The presence of three wires does not automatically mean the battery has a balance lead.

Can the Balance Lead Power the Device?

Normally, it should not be used as a substitute for the main power lead.

Balance wires and terminals are generally designed for voltage sensing and limited balancing current. Drawing the device’s full operating current through them may cause excessive voltage drop, connector heating, or wire damage.

An exception may exist when the battery uses an intentionally designed combined connector. In that case, every circuit and its permitted current must be defined in the battery specification.

What Does “JST Connector” Mean?

JST is a connector manufacturer, not the name of one universal connector.

The company offers many connector families with different:

• Contact pitches

• Housing dimensions

• Circuit counts

• Wire ranges

• Locking structures

• Board headers

• Current and voltage ratings

• Mounting directions

• Terminal designs

Describing a battery as having a “2-pin JST connector” is therefore incomplete. The description should identify the connector series and exact part number.

Common JST Families Used Around Battery Systems

These ratings are reference maximums under the manufacturer’s specified conditions. They are not universal safe operating currents for every battery design.

For example, rating changes may result from:

• Using a smaller wire

• Loading several adjacent circuits

• Operating at elevated temperature

• Using a different terminal or plating option

• Incomplete crimping

• Repeated vibration

• Contamination or corrosion

• Mating with a nonmatching or low-quality component

Is JST-XH Pitch 2.5 mm or 2.54 mm?

The official pitch of the JST XH series is 2.5 mm.

It is frequently described as 2.54 mm in marketplace listings, but 2.5 mm and 2.54 mm should not be treated as interchangeable dimensions without checking the actual components. Over several positions, even a small pitch difference can cause misalignment.

Are All White Battery Connectors JST?

No.

A white housing does not establish its manufacturer or series. Visually similar connectors may come from different brands or use different terminal structures and dimensions.

Before reproducing an existing battery connector, obtain at least one of the following:

• Exact manufacturer and series

• Housing and terminal part numbers

• Mating-header part number

• Dimensioned connector drawing

• Approved physical sample

• Device PCB or harness specification

Photographs alone are often insufficient for reliable identification.

What Does “Molex Connector” Mean?

Molex also manufactures many connector families rather than a single “Molex battery plug.”

Depending on the product, a Molex connector may be designed for compact signals, wire-to-board power, wire-to-wire power, communication, or combined power and data connections.

Examples that may be considered for battery systems include:

PicoBlade

PicoBlade is a compact 1.25 mm-pitch connector family used for space-constrained wire-to-board and wire-to-wire connections.

It may be suitable for:

• Low-current battery outputs

• Temperature-sensing circuits

• Identification lines

• Compact monitoring connections

• Small internal harnesses

Its current capability depends on wire size and circuit configuration. It should not be assumed to support a higher-current battery simply because the connector has two circuits.

Nano-Fit

Nano-Fit is a compact power connector family with locking, polarization, and multiple circuit options.

It can be considered when the application needs:

• More current than a miniature signal connector

• Positive mechanical retention

• Compact power delivery

• Multiple power or auxiliary circuits

• Protection against incorrect mating

The exact housing, terminal, wire, and circuit configuration must still be selected from the relevant product specification.

Micro-Fit and Other Power Families

Molex Micro-Fit and other power connector families may be used when an application needs a larger current path, stronger retention, or more circuit options.

The larger housing size should be evaluated against:

• Available PCB space

• Battery-compartment clearance

• Cable-bend radius

• Assembly access

• Required mating force

• Service and replacement needs

As with JST, “two-pin Molex” is not a production-ready connector specification.

JST vs Molex: Which Should You Choose?

Neither brand is automatically better for every LiPo battery.

The correct choice depends on the complete electrical and mechanical interface.

If the device already has a qualified PCB header, matching that interface may be the most practical option. For a new design, connector selection should be completed together with the battery, PCB, enclosure, charger, and assembly process.

How to Choose the Right LiPo Battery Connector

1. Confirm the Battery Configuration

Start with:

• Cell chemistry

• 1S, 2S, 3S, or another series configuration

• Parallel configuration

• Nominal and maximum charging voltage

• Battery capacity

• PCM or BMS arrangement

• Charging method

The pack configuration determines whether a separate balance connection is needed and how many sensing circuits are required.

Readers unfamiliar with LiPo construction can first review what a lithium polymer battery is.

2. Calculate the Actual Current Demand

Provide the battery supplier with:

• Normal operating current

• Maximum continuous current

• Peak current

• Peak duration

• Charging current

• Standby current

• Acceptable voltage drop

Do not select a connector using battery capacity alone. A 1000 mAh battery may power either a low-current sensor or a motor-driven device, and the two applications may require completely different connectors and wires.

3. Identify Every Required Circuit

Determine whether the battery needs:

• Main positive and negative

• Series-voltage taps

• NTC temperature sensing

• Battery identification

• Communication

• Charger detection

• Enable or control signal

• Separate charge and discharge paths

A wiring diagram is especially important when more than two conductors are present.

4. Confirm the Mating Component

Record the exact component on the device, charger, or PCB.

The connector specification should include:

• Manufacturer

• Series

• Housing part number

• Terminal part number

• Matching header or plug part number

• Number of circuits

• Pitch

• Mating direction

• Locking structure

• Keying or polarization

Providing only the battery-side connector can leave the supplier uncertain about the actual mating interface.

5. Define Polarity and Pinout

Polarity should never be assumed from wire color or a previous battery.

Specify the pinout using:

• Manufacturer terminal numbering

• A drawing of the connector’s mating face

• Latch or key orientation

• Wire color

• Electrical function

• Pack-side and device-side references

The viewing direction must be stated clearly. A pin arrangement can appear reversed when viewed from the wire-entry side instead of the mating face.

Before connecting a sample to valuable equipment, verify polarity and voltage with a suitable meter.

6. Select the Wire Gauge and Length

Wire selection should account for:

• Continuous and peak current

• Cable length

• Voltage-drop limit

• Flexibility

• Bend radius

• Available routing space

• Temperature rating

• Insulation thickness

• Terminal crimp range

The requested length should define its measurement reference, such as:

• From the battery pouch edge to the connector housing

• From the PCM edge to the housing

• Exposed wire length

• Total harness length

• Length including or excluding the connector

A tolerance should also be specified.

7. Evaluate Mechanical Retention

A friction-fit connector may be sufficient inside a stationary sealed product. It may be unsuitable for a replaceable battery, drone, robot, handheld tool, or wearable exposed to repeated movement.

Possible retention options include:

• Friction lock

• Positive latch

• Secondary lock

• Clip or bracket

• Strain-relief sleeve

• Adhesive or anchored harness

• Device-side cable clamp

The wire should not transfer repeated pulling force directly to the battery tabs, PCM solder joints, or crimp terminals.

8. Build and Test Samples

The connector should be evaluated as part of the complete battery system.

Sample validation may include:

• Connector fit and mating direction

• Polarity and pinout

• Contact resistance

• Voltage drop under maximum load

• Temperature rise

• Peak-current performance

• Charging compatibility

• Balance-voltage readings

• Pull and retention strength

• Cable routing

• Vibration performance

• Repeated mating

• Enclosure assembly

• Strain relief

• Device startup and shutdown behavior

ZERNE’s Li-polymer battery quality control system outlines the production and inspection controls that can support battery sample and shipment verification.

Custom LiPo Battery Connector Options

A custom connector request can involve more than changing the plastic housing.

Connector Housing and Terminal

The battery can be configured with:

• A specified JST series

• A specified Molex series

• Another recognized connector family

• A customer-supplied connector

• A device-specific wire harness

• Individual terminals

• Solder tabs

• Bare or pre-tinned wires

Exact part numbers should be used whenever possible.

Wire Gauge and Insulation

Wire size can be selected according to the current and terminal range. Insulation may also vary in:

• Outer diameter

• Temperature rating

• Flexibility

• Abrasion resistance

• Flame rating

• Material

• Color

The wire must fit both the connector terminal and the available routing space.

Cable Length and Exit Direction

Custom cable length helps the battery fit the enclosure without excessive slack or tension.

The design may also define:

• Wire-exit position

• Left, right, top, or bottom routing

• Fold direction

• Cable bundle arrangement

• Twisted wires

• Flat or round harness

• Attachment point

• Heat-shrink position

These details are particularly important in thin devices where the cable cannot cross the battery surface or interfere with the enclosure.

Pinout and Wire Color

A supplier can reproduce a customer-defined pinout, but the requirement should be documented instead of communicated only through a photograph.

For multi-pin connectors, define every circuit individually:

This is only an example. The actual order must match the device design and connector drawing.

Balance Harness

For multi-series packs, custom options may include:

• Balance-connector series

• Number of circuits

• Wire length

• Wire color sequence

• Pin order

• Combined or separate balance connector

• Connector location

• BMS integration

• Charger compatibility

The balance harness should be verified against the actual charger or BMS before use.

NTC, Identification, and Communication Wires

Compact electronic products may require additional circuits for:

• NTC temperature monitoring

• Battery identification resistance

• Fuel-gauge communication

• SMBus or other digital communication

• Enable signals

• Authentication

• Charge control

These circuits should not be described simply as “extra wires.” Their electrical function, component values, reference voltage, and pin assignment should be included in the battery specification.

Mating Connector and Preassembled Harness

A battery supplier may provide:

• Battery-side connector only

• Mating connector components

• A completed device-side harness

• A charger adapter

• An extension lead

• A test lead

• A custom transition harness

Including the mating connector can reduce sourcing uncertainty, but the device manufacturer should still verify that the supplied part matches the PCB and assembly process.

Labeling and Identification

Custom harnesses may use:

• Wire labels

• Connector labels

• Polarity markings

• Color coding

• Part numbers

• Batch identification

• Protective caps

Color coding improves assembly efficiency, but it should support—not replace—the documented pinout.

ZERNE supports connector, cable length, PCM/BMS, NTC, voltage, capacity, and pack-structure customization through its custom battery solutions.

Information to Provide for a Custom Connector Quote

The following information helps a battery manufacturer evaluate the connector correctly.

Battery Information

• Battery chemistry

• Cell and pack configuration

• Nominal voltage

• Maximum charging voltage

• Capacity

• Battery dimensions

• PCM or BMS requirement

Electrical Information

• Normal operating current

• Maximum continuous current

• Peak current and duration

• Charging current

• Permitted voltage drop

• Required sensing or communication circuits

Connector Information

• Manufacturer

• Connector family

• Exact housing part number

• Terminal part number

• Mating component

• Circuit count

• Pitch

• Pinout

• Polarity

• Locking requirement

Wire Information

• Wire gauge

• Insulation type

• Wire colors

• Cable length

• Length tolerance

• Wire-exit direction

• Strain-relief requirement

Application Information

• Device type

• Available installation space

• PCB or enclosure drawing

• Operating temperature

• Vibration and movement conditions

• Expected mating cycles

• Target market

• Sample and production quantity

If the exact connector part number is unknown, provide a physical mating sample, detailed dimensions, and clear photographs from several directions. The part should still be confirmed before mass production.

Common LiPo Battery Connector Mistakes

Connector Inspection Before Production and Shipment

Connector quality should be checked during both sample approval and production.

Important inspection points include:

• Correct housing and terminal part numbers

• Correct wire gauge and insulation

• Accurate cable length

• Correct wire color

• Correct polarity and pinout

• Complete terminal insertion

• No backed-out terminals

• Proper crimp height and conductor capture

• No cut strands

• No exposed conductors

• Secure solder joints where applicable

• Correct heat-shrink position

• Adequate strain relief

• Clean housing without deformation

• Reliable mating and locking

• Stable voltage under load

For shipping, exposed battery connectors should be protected from contact with metal or other conductive materials. A connector cap, individual nonconductive packaging, or another suitable isolation method may be required.

Conclusion

A LiPo battery connector should be treated as part of the electrical system, not as a minor accessory selected after the battery is finished.

The main lead must support the battery’s continuous current, peak current, charging current, and voltage-drop limits. A balance lead serves a different purpose by giving a charger or BMS access to individual series-group voltages. Additional wires may carry temperature, identification, or communication signals.

JST and Molex are connector manufacturers with many different product families. A reliable specification should therefore include the exact series, housing, terminal, pitch, circuit count, mating part, wire gauge, length, polarity, and pinout.

Before mass production, test the battery and connector inside the real device at maximum expected load. Confirm fit, temperature rise, voltage drop, cable routing, retention, charging, and polarity. These checks help ensure that the selected lithium polymer battery can integrate reliably with the final product.

Frequently Asked Questions

What is the main connector on a LiPo battery?

The main connector carries power between the battery and the device and usually also carries charging current. It must be selected according to continuous current, peak current, wire size, voltage drop, and mechanical requirements.

What is a LiPo balance connector used for?

A balance connector gives a charger or BMS access to the voltage of each series-connected cell group. It is mainly used for cell monitoring and balancing rather than powering the device.

How many wires should a balance lead have?

A conventional balance lead normally has one more wire than the pack’s series count. For example, a 3S pack usually has four balance wires.

Does a 1S LiPo battery need a balance connector?

Usually not, because a 1S battery has only one voltage group. A third wire on a 1S battery is more likely to be an NTC, identification, or communication wire.

Are JST-PH and JST-XH connectors interchangeable?

No. JST-PH has a 2.0 mm pitch, while JST-XH has a 2.5 mm pitch, and their housings and headers are different. The exact series and part number must match.

Can the same LiPo connector have reversed polarity?

Yes. Similar or physically compatible connector housings may be wired with different polarity. Always verify the pinout and voltage before connecting a replacement battery.

Can a LiPo battery connector be customized?

Yes. Connector series, pinout, wire gauge, cable length, wire color, exit direction, balance lead, NTC, communication wires, mating harness, and strain relief can all be customized for an OEM device.