How to Choose a Connector for a Custom Lithium Battery Pack

The connector is the electrical and mechanical interface between a custom lithium battery pack and the host device. It carries power, affects voltage drop, determines how the battery is installed, and may also provide balance, temperature-sensing or communication connections.

For OEM projects, connector selection should take place at the same time as battery pack design. A connector that fits the current prototype may still create problems during mass production if it is difficult to assemble, lacks a reliable locking mechanism, increases enclosure height or does not match the final charger and BMS architecture.

When developing a custom battery, ZERNE can configure the pack around the required connector type, cable length, wire-exit position and application conditions. You can review the broader custom lithium battery pack solutions before preparing a connector specification.

Quick Answer: How Do You Choose a Battery Pack Connector?

Choose a battery pack connector by checking these requirements in order:

1. Confirm the battery voltage and the maximum continuous and peak current.

2. Define whether the connector carries discharge power, charging power or both.

3. Confirm the number of power, balance, temperature-sensing and communication pins.

4. Check the mating connector, pitch, height, width, locking method and keying.

5. Select the wire gauge according to current, cable length, flexibility and temperature rise.

6. Verify polarity, pin assignment, contact resistance and protection against incorrect mating.

7. Validate the complete battery, connector, cable and host-device assembly under realistic conditions.

A connector should not be selected from the battery capacity in mAh alone. A 2,000mAh pack may require very different connector and wire specifications depending on whether the device draws 1A continuously, 8A intermittently or has a high start-up current.

1. Start With the Device Interface, Not the Connector Brand

The host device usually defines the first connector constraints. Before comparing connector families, document how the battery will connect to the product.

Important questions include:

This information prevents a common design error: choosing a familiar connector first and trying to adapt the battery pack around it later.

For a detailed overview of how connectors fit into the wider battery specification, see the guide to lithium-ion battery pack design. The connector decision here is narrower: it focuses on the interface between the finished battery pack and the device.

2. Define the Electrical Requirements

Nominal voltage and maximum voltage

The connector must be compatible with the pack’s operating voltage and the highest voltage that can appear during charging. The relevant value is not only the nominal battery voltage.

For example, a typical lithium battery cell may be described by a nominal voltage of 3.7V, while its fully charged voltage is higher. A multi-cell pack increases the voltage seen by the connector and cable assembly.

The connector specification should therefore include:

• nominal battery voltage;

• maximum charging voltage;

• expected operating voltage range;

• discharge cutoff voltage where relevant;

• whether the connector is used for charging, discharging or both.

The connector itself may have a voltage rating, but the complete assembly must also be checked for insulation, spacing, pin-to-pin arrangement and the host device’s electrical design.

Continuous current

Continuous current is the current expected during normal operation. It is usually the first value used to screen the connector and cable.

A basic estimate for a DC load is:

Current ≈ Power ÷ Voltage

If a device consumes 18W from a nominal 7.4V battery pack:

18W ÷ 7.4V ≈ 2.43A

The actual battery-side current may be higher when a converter is used because of conversion losses:

Battery current ≈ Output power ÷ (Battery voltage × Converter efficiency)

The connector should be evaluated using the actual current path, not only the nominal output power of the device.

Peak and inrush current

Some devices draw a short-duration peak current when a motor starts, a radio transmits, a pump activates or a processor changes operating mode. A connector suitable for the average current may still experience excessive voltage drop or heating during these events.

Document:

• normal operating current;

• maximum continuous current;

• peak current;

• peak duration;

• repetition frequency;

• start-up or inrush current.

Do not use a connector’s headline current value without checking how that value was determined. Ratings may depend on ambient temperature, terminal arrangement, wire size, number of energized contacts and allowable temperature rise.

3. Match the Connector to the Current Path

A custom lithium battery pack may contain several electrical paths:

• main positive and negative discharge leads;

• charging leads;

• balance leads;

• NTC or temperature-sensing wires;

• communication lines;

• identification or interlock circuits.

Not every battery requires all of these connections. The connector should be selected according to the actual system architecture.

Main power connector

The main connector carries the highest current and normally requires the most attention to:

• terminal contact resistance;

• wire cross-sectional area;

• mating reliability;

• locking strength;

• polarity protection;

• temperature rise;

• cable flexibility.

Balance or sense connector

A balance connector may carry lower current but still requires accurate pin assignment and reliable contact. It may connect individual cell-tap wires to a charger or battery management system.

The balance connector should not be treated as a substitute for the main power connector. It has a different electrical function and may require different wire sizes, pin spacing and handling procedures.

Temperature and communication pins

A smart battery pack may use additional pins for an NTC, SMBus, CAN, UART or another signal interface. These pins need correct assignment, signal integrity and protection from accidental shorting.

The connector selection should be coordinated with the BMS architecture. For a broader explanation of the protection-system decision, see PCM vs. BMS for LiPo batteries.

4. Check Contact Resistance and Voltage Drop

A connector is part of the power circuit. Even a small resistance can become important at higher current.

The basic relationship is:

Voltage drop = Current × Resistance

The heat generated in the connector contact path can be estimated as:

Power loss = Current² × Resistance

For example, if the total contact-path resistance is 10mΩ and the current is 6A:

Voltage drop = 6A × 0.010Ω = 0.06V
Power loss = 6² × 0.010Ω = 0.36W

These calculations are preliminary. The final result depends on the complete connector, terminal, crimp, wire, mating interface and operating temperature.

High contact resistance can cause:

• lower voltage at the device;

• reduced motor or actuator performance;

• additional heating;

• reduced efficiency;

• localized temperature rise;

• unstable operation during peak loads.

For devices with strict low-voltage limits or high current demand, contact resistance should be included in the prototype test plan rather than evaluated only from a catalogue rating.

5. Choose the Correct Wire Gauge

The battery pack connector and cable must be selected as one assembly. A high-current connector does not compensate for an undersized cable.

Wire-gauge selection depends on:

• continuous current;

• peak current;

• cable length;

• allowable voltage drop;

• ambient temperature;

• insulation temperature rating;

• cable flexibility;

• available enclosure space;

• routing and bending conditions.

In the AWG system, a smaller AWG number generally indicates a larger conductor. However, an AWG number by itself is not enough to validate a design. The final current capability depends on the cable construction, insulation, temperature and installation conditions.

Longer cables create more resistance and therefore more voltage drop. Flexible equipment may need a different cable construction from a fixed industrial assembly even when both carry the same current.

The battery manufacturer should receive the required cable length and wire-exit position, not only the connector name. ZERNE’s custom battery service lists cable length, connector type and wire-exit position as configurable project inputs.

6. Consider Connector Size, Locking and Keying

Electrical compatibility does not guarantee mechanical compatibility.

Connector dimensions

Check the complete installed envelope:

• connector body height;

• connector width and length;

• terminal clearance;

• cable bend radius;

• latch clearance;

• space for insertion and removal;

• interference with the battery pouch, case or BMS;

• access for production assembly.

A connector that fits the battery but cannot be inserted after the enclosure is assembled will create a manufacturing problem.

For battery-powered products with tight compartments, connector dimensions should be evaluated alongside the battery compartment design, including clearance, cable routing and allowance for the finished pack.

Locking and retention

A friction-fit connector may be adequate for a protected internal assembly. Equipment exposed to vibration, movement or repeated service may require a positive latch or another retention method.

Ask:

• Can vibration loosen the connection?

• Can the operator disconnect it accidentally?

• Is the locking mechanism accessible after installation?

• Can the connector be released without damaging the cable?

• Does the latch remain secure after repeated mating cycles?

Keying and polarity protection

Keying helps prevent incorrect mating. Polarity protection reduces the risk of connecting the battery in reverse.

A connector system should have a clearly documented:

• positive terminal;

• negative terminal;

• signal-pin order;

• balance-wire order;

• temperature-sensor pin;

• communication pin;

• unused-pin treatment.

Never rely on wire color alone. The approved drawing or wiring table should define the pinout.

7. Select the Connector Type for the Application

JST, Molex and other wire-to-board or wire-to-wire connector families may be suitable for different battery applications. Custom connector assemblies may also be appropriate when the device has unusual space, cable or integration requirements.

The key question is not “Which brand is best?” It is:

Which connector architecture provides the required electrical performance, mechanical retention and production reliability for this device?

A compact wearable device may prioritize:

• low profile;

• small pitch;

• flexible cable routing;

• low insertion force;

• limited current.

An industrial device may prioritize:

• higher current capability;

• stronger retention;

• thicker cable;

• vibration resistance;

• easier service replacement.

A medical or monitoring product may require:

• controlled pin assignment;

• reliable identification;

• protected signal contacts;

• documented assembly and inspection procedures.

For terminology such as main lead, balance lead, JST, Molex and custom connector options, readers can refer to the existing LiPo battery connector explanation. The selection decision should then return to the device’s current, mechanical and validation requirements.

8. Coordinate the Connector With the Charger and BMS

The connector design must match the complete battery system.

Important coordination points include:

• charging current;

• discharge current;

• cell count;

• balance requirements;

• temperature sensing;

• overcurrent protection;

• undervoltage and overvoltage protection;

• communication protocol;

• charger-side pin assignment;

• separation of charging and discharge paths.

For example, a battery pack may use one connector for power and another for balancing or communication. In other designs, the host device and charger may share a multi-pin interface. The correct solution depends on the BMS, charger and device architecture.

The connector should be frozen only after the following are agreed:

1. battery cell configuration;

2. protection strategy;

3. charger interface;

4. host-device pinout;

5. cable length and exit location;

6. charging and discharging limits.

A connector cannot correct an incompatible charger or an incorrectly configured protection system.

9. Prepare a Connector Specification for the Battery Manufacturer

A clear connector request helps the manufacturer evaluate feasibility and prepare an accurate sample.

Provide the following information:

The battery manufacturer may recommend a different connector if the requested option does not meet the current, space or production requirements. The substitution should be approved using an updated drawing, sample and pinout confirmation.

10. Validate the Connector During Prototype Testing

Connector validation should be part of battery-pack sample approval, not an afterthought.

A practical OEM validation plan may include:

Electrical checks

• verify polarity and pin assignment;

• check continuity;

• measure voltage drop under representative current;

• check contact resistance where applicable;

• confirm charging and discharging paths;

• verify balance and temperature-sensing connections;

• observe connector temperature during normal and peak operation.

Mechanical checks

• confirm mating and unmating force;

• inspect latch engagement;

• check cable strain relief;

• verify connector clearance in the enclosure;

• inspect cable bending and routing;

• test repeated mating if the product is serviceable.

Environmental and system checks

• evaluate operation under the intended temperature range;

• check performance under vibration or movement;

• inspect for intermittent contact;

• verify the connector after transport or handling;

• confirm that the finished battery pack does not interfere with the enclosure.

For a broader sample-approval process, see How to Validate a Custom LiPo Battery Sample Before Mass Production.

11. Common Battery Connector Selection Mistakes

Choosing by capacity only

Capacity indicates how much charge the pack stores. It does not define the required connector current, cable size or peak-load performance.

Matching only the plug shape

Two connectors may appear similar while having different pinouts, terminal sizes, locking methods or current capabilities.

Ignoring the charging path

A connector used for both charging and discharging must be evaluated for the highest current in either direction.

Using a connector without checking cable routing

The connector may fit the PCB or battery case but fail when the cable needs to bend around the enclosure.

Relying on wire color

Wire color can vary by supplier or assembly. Use a controlled pinout drawing and verify the finished sample.

Selecting an oversized connector without checking the enclosure

A connector with greater current capability may also require more height, clearance and bend radius. The mechanical cost can exceed the electrical benefit.

Waiting until mass production

Changing the connector after tooling, cable fixtures or enclosure validation may affect the battery pack, host device and production process simultaneously.

12. Battery Pack Connector Selection Checklist

Before approving a custom lithium battery connector, confirm:

• Host-side mating connector identified.

• Nominal and maximum voltage confirmed.

• Continuous, peak and inrush current documented.

• Charging and discharging paths defined.

• Main power and signal pins identified.

• Balance, NTC or communication requirements confirmed.

• Connector dimensions fit the enclosure.

• Cable length and exit position approved.

• Wire gauge and voltage-drop target defined.

• Polarity and keying checked.

• Locking and strain-relief requirements confirmed.

• Pinout drawing reviewed.

• Prototype sample electrically tested.

• Mechanical retention and cable routing validated.

• Production assembly and inspection method agreed.

FAQ

What is the most important factor when choosing a battery pack connector?

Current is one of the most important factors, but it should be evaluated together with voltage, contact resistance, wire gauge, mechanical retention, pinout and operating environment.

Can I use the same connector for charging and discharging?

Sometimes, but only when the connector, cable, charger, BMS and host device are designed for the combined current path. Separate charging and discharge paths may be more appropriate for some systems.

Is a JST connector suitable for a lithium battery pack?

A JST connector may be suitable for certain compact or lower-current applications, but suitability depends on the exact series, terminal arrangement, wire size, current profile and mechanical conditions. The connector name alone is not enough for approval.

Do I need a balance connector?

A balance connector is required only when the battery architecture and charger or BMS need individual cell connections. It should not be added without confirming the cell configuration and protection design.

How do I specify the connector to a battery manufacturer?

Provide the host connector part number, voltage, continuous and peak current, cable length, wire gauge, pinout, cable-exit position, available space, locking requirement and expected validation tests.

Should the connector be selected before the battery pack is designed?

The connector should be defined early, but it should be finalized together with the cell configuration, BMS, charger, enclosure and cable routing. Early coordination reduces redesign risk.

Conclusion

Choosing a connector for a custom lithium battery pack is an interface-engineering decision, not simply a component-selection task. The correct solution must carry the required current, maintain acceptable voltage drop, fit the enclosure, prevent incorrect mating and remain reliable during production and service.

OEM teams should provide the battery manufacturer with the host connector, current profile, pinout, cable requirements, mechanical envelope and validation conditions. The connector can then be integrated with the battery cells, BMS, charger and pack housing as one tested assembly.

For a project requiring a custom battery pack with a specified connector, cable length or wire-exit position, contact ZERNE’s custom battery team or review the broader lithium battery pack manufacturing and design solutions.