When developing a new electronic product, choosing a suitable lithium polymer battery pack is about much more than specifying voltage and capacity. A custom LiPo battery pack needs to match the device's electrical requirements, available space, operating environment, charging system, protection requirements, and mechanical interface.

For OEM and ODM projects, providing complete battery information at the beginning can help the battery manufacturer evaluate the design more efficiently and reduce unnecessary prototype changes. Industry design guidance also recommends defining voltage, current, capacity, mechanical dimensions, protection electronics, wiring, connectors, and applicable standards early in the development process.

1. Start With the Application

The first step is to understand what the battery will power and how the device will be used.

For example, a battery for a wearable device may prioritize:

• Small size

• Low weight

• Thin profile

• Moderate capacity

A battery for an industrial device may require:

• Higher discharge current

• Longer operating time

• Wider temperature range

• More robust protection

A medical or portable electronic device may have additional requirements for reliability, protection, testing, and documentation.

Before contacting a battery manufacturer, provide a basic description of:

• Device type

• Main application

• How the device operates

• Expected operating time

• Charging frequency

• Indoor or outdoor use

• Normal and extreme operating conditions

This information helps the battery engineer understand the application instead of designing the battery from specifications alone.

2. Specify the Required Voltage

Nominal voltage is one of the most important electrical parameters.

For many conventional LiPo applications, a single cell has a nominal voltage around 3.7V. Multiple cells can be connected in series when a higher pack voltage is required.

For example:

The exact voltage range and charging voltage should be determined by the selected cell chemistry and manufacturer's specifications.

When requesting a custom battery, don't only provide the nominal voltage. If available, also provide:

• Normal operating voltage

• Maximum voltage

• Minimum operating/cut-off voltage

• Required charging voltage

For a multi-cell battery, the series/parallel configuration should also be defined or discussed with the battery engineer.

3. Define the Required Capacity

Battery capacity is normally expressed in mAh or Ah.

For example:

• 500mAh

• 1000mAh

• 2000mAh

• 5000mAh

Capacity is closely related to the required runtime, but simply asking for the largest possible capacity is not always the right approach.

A basic estimation is:

Runtime ≈ Capacity (Ah) ÷ Average Current (A)

For example, if a device consumes an average of 500mA and uses a 2000mAh battery:

2Ah ÷ 0.5A ≈ 4 hours

Actual runtime can differ because of device efficiency, discharge conditions, temperature, battery characteristics, and the device's voltage cut-off.

Therefore, when customizing a battery pack, it is useful to provide both:

Target capacity + Required runtime

If you are unsure about the exact capacity, providing the device's average current consumption and expected operating time allows the battery manufacturer to help estimate a suitable capacity.

4. Provide the Maximum Battery Dimensions

For custom LiPo batteries, physical dimensions can be just as important as electrical specifications.

The manufacturer normally needs the maximum available:

Length × Width × Thickness

For example:

Maximum battery size: 50 × 30 × 6 mm

However, don't measure only the empty cavity. Consider the complete battery assembly, including:

• Pouch cell

• Tabs

• PCM/BMS

• Wires

• Connector

• Insulation

• Mechanical fixing

• Required clearance

A battery that meets the voltage and capacity requirements may still be unsuitable if the complete assembly cannot fit inside the product.

If available, providing a mechanical drawing, CAD file, enclosure drawing, or existing battery sample can make the design process much easier.

Tip: Tell the manufacturer the maximum dimensions

Instead of saying:

We need a 2000mAh battery.

It is much more useful to say:

We need a 3.7V battery around 2000mAh. Maximum dimensions are 8 × 40 × 50 mm.

This gives the engineer a much clearer starting point.

5. Provide the Current Requirements

Capacity and current are two different parameters.

A 2000mAh battery does not automatically mean that it can supply every type of 2A or 5A load.

The manufacturer should know:

• Average operating current

• Continuous discharge current

• Peak discharge current

• Peak duration

• Startup current, if applicable

For example:

Average current: 500mA
Peak current: 2A for 5 seconds

This information can be particularly important for products containing:

• Motors

• Wireless communication modules

• Pumps

• Heating elements

• High-power LEDs

• Drones

• Robotics

• Industrial equipment

A battery pack designed only according to mAh may not perform properly if the application has significant current peaks.

6. Specify the Battery Configuration

For a multi-cell LiPo pack, the manufacturer needs to know—or help determine—the required series and parallel configuration.

Series connection

Series connection increases voltage.

For example:

2 × 3.7V cells in series = approximately 7.4V nominal

Parallel connection

Parallel connection increases capacity and current capability.

For example:

2 × 2000mAh cells in parallel = approximately 4000mAh

Series + parallel

A 2S2P battery pack uses four cells and combines series and parallel connections.

The final configuration depends on the required voltage, capacity, current, available space, and cell characteristics.

If you don't know whether your project needs 1S, 2S, 2S2P, or another configuration, simply provide the device's electrical requirements and let the battery engineer evaluate the appropriate configuration.

7. Define PCM or BMS Requirements

A custom LiPo battery pack may require a PCM (Protection Circuit Module) or BMS (Battery Management System).

Depending on the design, protection functions can include:

• Overcharge protection

• Over-discharge protection

• Overcurrent protection

• Short-circuit protection

• Temperature monitoring

• Cell balancing for applicable multi-cell designs

• Battery status monitoring or communication

The exact protection design should match the battery chemistry, configuration, load, charger, and application.

For a simple battery pack, a PCM may provide the required protection functions. More complex multi-cell or smart battery applications may require a BMS with balancing, monitoring, or communication functions.

If your device already has a BMS

Tell the battery manufacturer.

In some applications, the device itself controls battery management, while in others the protection electronics need to be integrated directly into the battery pack.

8. Specify the Connector and Wire

The connector is a small component, but it can become a major issue during prototype testing if it is not specified correctly.

Provide:

• Connector brand, if required

• Connector model/part number

• Number of pins

• Wire length

• Wire gauge

• Wire type

• Polarity

• Pin configuration

For example:

UL1007 28AWG, 50mm, red/black, PH2.0 2-pin

If you already have a connector on your PCB, providing the connector model or drawing is preferable to simply saying "2-pin connector."

Battery design guides also recommend defining cable specifications, connector type, and pin configuration during the design stage.

9. Tell the Manufacturer About the Charger

The battery and charger need to be compatible.

If you already have a charger, provide:

• Charger model

• Charging voltage

• Charging current

• Charging method

• Charger specifications

If the charger is still under development, provide your desired charging time or maximum charging current.

For example:

Battery: 3.7V 2000mAh
Target charging time: approximately 2–3 hours

The battery manufacturer can then evaluate whether the requested charging conditions are appropriate for the selected cell and protection design.

10. Define the Operating Temperature

Temperature requirements should be discussed early in the project.

Provide, where applicable:

• Operating temperature

• Charging temperature

• Storage temperature

• Minimum temperature

• Maximum temperature

For example:

Operating: 0°C to 45°C
Charging: 5°C to 45°C

Temperature can affect usable capacity, voltage behavior, charging, battery life, and the appropriate cell selection.

This is particularly important for:

• Outdoor equipment

• Industrial devices

• Automotive applications

• Medical equipment

• Cold-storage equipment

• Devices used in hot environments

  

11. Consider the Mechanical Installation

A custom battery pack may need more than the correct dimensions.

Also consider:

• Mounting method

• Adhesive

• Brackets

• Screw holes

• Cable exit position

• Connector location

• Battery orientation

• Enclosure

• Vibration

• Shock

• Available clearance

For example, two battery packs with identical electrical specifications may have completely different mechanical designs if one requires the connector to exit from the top and the other from the side.

If your product has a tight enclosure, a 3D CAD drawing can be extremely useful.

12. Define the Required Certifications and Documents

The required certifications and transportation documents depend on the product, market, battery design, and shipping method.

Depending on the project, customers may request documents or testing related to standards such as:

• UN 38.3

• IEC 62133

• UL requirements

• CE

• RoHS

• MSDS/SDS

Not every battery requires every certification, so requirements should be confirmed according to the destination market and application.

It is better to discuss certification requirements before the battery design is finalized, because testing and documentation can affect cell selection, protection design, samples, cost, and project timing.

13. Provide Prototype and Production Quantities

For a commercial battery project, the manufacturer may also need to know:

• Sample quantity

• Prototype quantity

• Expected first order quantity

• Estimated annual demand

• Expected mass-production schedule

For example:

Prototype: 10 pcs
First production order: 5,000 pcs
Estimated annual demand: 30,000 pcs

This information helps the manufacturer evaluate the appropriate development and production approach.

It can also be useful when discussing custom components such as PCM/BMS, connectors, housings, labels, and packaging.

14. A Complete LiPo Battery Customization Checklist

Before requesting a quotation, you can prepare the following information:

You don't need to have every item finalized before contacting a battery manufacturer. If some specifications are unknown, providing the device requirements and constraints allows the engineering team to help determine the remaining parameters.

What If You Don't Know All the Specifications?

This is actually quite common, especially during the early stages of product development.

You don't necessarily need to tell a battery manufacturer:

"I need a 3.7V 2500mAh battery."

Instead, you can provide:

Device voltage: 3.7V
Average current: 600mA
Peak current: 1.5A
Required runtime: 4 hours
Maximum battery size: 10 × 45 × 60 mm
Connector: 2-pin
Operating temperature: 0–45°C

The manufacturer can then evaluate suitable cell dimensions, capacity, protection design, wiring, and connector configuration.

This application-based approach is particularly useful when the battery is being developed at the same time as the electronic device.

Final Thoughts

A successful custom LiPo battery pack starts with a complete understanding of the device, rather than simply selecting a cell with a certain capacity.

The key information includes:

Application → Voltage → Capacity → Current → Dimensions → Configuration → PCM/BMS → Connector → Charging → Temperature → Certifications → Quantity

The more accurately these requirements are defined, the easier it is for a battery manufacturer to recommend an appropriate cell and develop a battery pack that fits both the electrical and mechanical requirements of the product.

For OEM and ODM projects, it is also a good idea to involve the battery manufacturer during the early product-design stage. This allows the battery dimensions, protection circuit, connector, charging system, and installation method to be considered together rather than redesigned later.