Battery Pack Design

How to Prepare a Custom Lithium Battery Pack RFQ: An OEM Buyer’s Practical Guide

custom lithium battery packReviewed by Clara11 min read

A practical checklist for turning an application brief into a quote-ready custom lithium battery pack RFQ.

Illustrative visual. Final configuration and documentation scope are assessed per project.

A custom lithium battery pack RFQ is not simply a request for a price. It is the first engineering and procurement document in a project that may involve a new device, an industrial retrofit, a medical product, a mobile robot, or an upgraded power system. The quality of the first brief determines whether a supplier can give a useful technical response, identify risks early, and quote a configuration that can actually fit the product.

For OEM buyers, the most common delay is not cell availability. It is a missing requirement: a peak current was never stated, the space envelope arrived late, the charging method was assumed, or the target market was mentioned only after sample work started. Those omissions can affect cell selection, series and parallel arrangement, BMS limits, cable routing, enclosure design, documentation review, and shipment preparation.

This guide explains what to send to a custom lithium battery pack manufacturer before asking for a quote. It is written for product managers, sourcing teams, and engineers who need an actionable starting point without pretending that a preliminary brief is a finished battery specification.

Describe what the equipment does

The first question should be: what must the equipment do between charges? “We need a 24 V pack” is a starting point, not a design brief. A battery used in an AGV may experience traction peaks, repeated acceleration, standby drain, and regenerative behavior. A portable medical device may have a lower average load but tighter expectations around available space, charge indication, serviceability, and documentation. A telecom backup product may prioritize standby duration and installation method.

Describe the equipment in plain language and attach what already exists:

• Product name or internal project name.
• How the device is used during a typical shift, procedure, route, or day.
• Whether the load is steady, pulsed, intermittent, motor-driven, or communication-heavy.
• Operating environment: indoor or outdoor, vibration, dust, ventilation, ambient temperature, moisture exposure, and installation orientation.
• Whether the pack is replaceable, fixed inside the equipment, or charged in a dock.

This context prevents a false comparison between batteries that share a nominal voltage but face very different demand. It also helps the manufacturer decide which questions should be answered before a quotation is treated as a release-ready configuration.

Explain the duty cycle

Duty cycle is often more useful than a single “working hours” statement. For example, an equipment team may describe a 30-minute operating period followed by a 15-minute charge, eight times per day. Another project may run continuously with short, high-current motor events. These patterns influence thermal assessment, current capability, charging strategy, and realistic runtime expectations.

If measured data are available, send them. A current trace, controller log, bench-test record, or even a list of measured current at different operating modes is more informative than a generic “high power” label. If data are not available, state that clearly. A responsible supplier can then propose a measurement plan rather than filling the gap with an unsupported performance claim.

Voltage is a system requirement

State the device input-voltage range, not only its nominal label. The battery, BMS, charger, motor controller, DC/DC converter, and low-voltage cutoff all need to work together. A pack’s voltage changes during charge and discharge, so the relevant question is whether the equipment accepts the complete operating range.

Useful RFQ inputs include:

Capacity is not the only runtime input

Capacity is commonly stated in ampere-hours, but the equipment consumes energy. A more complete brief links runtime to load, voltage, and use conditions. If you know the device’s power or energy use, share it. If you only know the existing battery capacity and actual working time, that is still valuable comparison data.

Avoid asking a supplier to guarantee runtime before the application conditions are defined. Runtime can change with load profile, ambient temperature, charging state, equipment efficiency, and aging. An honest estimate should document its assumptions; it should not turn a marketing number into a field guarantee.

Separate continuous current from peak current

This is one of the highest-value details in a custom pack RFQ. A pack can support an application’s average energy demand and still fail at a brief start-up peak. Typical causes include motor inrush, actuator movement, compressor start, radio transmission bursts, or simultaneous operation of several subsystems.

State the peak current, its duration, frequency, and whether it occurs near a low state of charge. If no measurement is available, identify the load type and controller. During a factory test, this information guides the test profile; during installation preparation, it guides cable, connector, and protection discussions.

Send the available space early

An enclosure can be technically capable yet impossible to install because cable exit, mounting points, service clearance, or connector access were considered too late. Send a 2D drawing, CAD envelope, annotated product photograph, or a simple hand sketch with dimensions. Include tolerances where space is tight.

For a useful mechanical review, identify:

• Maximum length, width, and height.
• Restricted zones, screw bosses, airflow paths, and display or service areas.
• Mounting method and expected vibration or shock exposure.
• Cable length, exit direction, and connector accessibility.
• Target ingress protection or enclosure expectations, if applicable.
• Weight target or handling constraints.

Do not assume a rectangular envelope tells the whole story. A small obstruction, bend radius, or connector latch can change the most practical layout. Early visuals prevent samples that look correct on a bench but cannot be assembled into the finished device.

Be clear about replaceability and service

Ask whether the pack must be field-replaceable, internally serviced, permanently installed, or removable only by trained personnel. This affects the connector, latch, enclosure, labeling, instructions, and shipment configuration. It can also affect how the product team plans installation preparation and after-sales support.

The BMS is part of the battery pack design, not an optional afterthought. At a minimum, discuss protection behavior for charge, discharge, current, temperature, and short circuit. The final functions should be selected against the pack chemistry, series count, load behavior, charger, and application risk—not copied from another product without review.

For connected equipment, state whether the host needs battery data such as pack voltage, current, temperature, state of charge, fault status, or cycle information. If CAN, SMBus, UART, RS485, or another interface is expected, attach the protocol or provide the owner who can answer integration questions. A communications request that arrives after the mechanical design can create avoidable rework.

Questions to include in the RFQ

1. Does the application need only protection, or host-visible data as well?
2. Is there a defined charger and charge-voltage limit?
3. Should the pack wake automatically, use a switch, or respond to a dock?
4. Are there low-temperature, high-temperature, or storage conditions that affect charging?
5. Does the host require a specific connector pinout or communication protocol?

Documentation must match the finished pack

Buyers frequently ask whether a supplier “has certificates.” The more useful question is which documentation applies to the final configuration, destination, and shipment method. A test record or certificate associated with a different pack, chemistry, configuration, or market is not evidence that it applies to your project.

State the destination country or region, intended product category, whether the pack ships alone or with equipment, and the anticipated transport route. For lithium batteries, transport requirements can differ based on the battery type, watt-hour rating, packing arrangement, and mode of transport. IATA notes that manufacturers and subsequent distributors must make the UN 38.3 test summary available for applicable lithium cell or battery types; shipping obligations still need to be checked against the final product and transport plan. [IATA guidance](https://www.iata.org/en/publications/newsletters/iata-knowledge-hub/what-to-know-about-how-to-ship-lithium-batteries/)

This is also where a buyer should ask what documentation can be provided for review and at which project stage. It is more credible to say “documentation applicability will be assessed for the final configuration” than to imply that one generic document covers every pack.

Plan shipment inspection

Before a production shipment, align on what the shipment inspection should cover: product identification, visible condition, configuration confirmation, labeling, pack quantity, accessories, packaging, and any agreed release documentation. A shipment inspection is not a substitute for product validation, but it helps prevent preventable mismatch between the approved configuration and the dispatch.

Forecast quantity affects sourcing, production planning, tooling choices, packaging, and the practical route from sample to production. State the expected sample quantity, pilot quantity, annual forecast, reorder pattern, and target date if known. A realistic range is better than a precise but unsupported number.

Also tell the supplier whether the project is at concept, prototype, validation, or production stage. The right first response for a concept-stage project may be a requirement checklist; for a validated product, it may be a configuration and documentation review. Both are legitimate, but they are not the same request.

You do not need a perfect specification to start a useful battery discussion. Send the application, target voltage, runtime expectation, available space, target market, and any drawing or photo you have. The remaining questions can be prioritized during technical review.

Use this template in an email or enquiry form:

```text

Application / equipment:

Current battery or reference product:

Target voltage and acceptable input range:

Required runtime or energy target:

Continuous current / power:

Peak current / duration / frequency:

Charging method and charger details:

Available installation space and drawing/photos:

Connector, cable, and mounting requirements:

BMS protection and communication requirements:

Operating and storage environment:

Target market and shipment arrangement:

Documentation requested:

Sample quantity / forecast quantity / required date:

Project contact and technical contact:

```

Can I request a quote before I have a final drawing?

Yes. Provide the best available dimensions, annotated photos, or a preliminary enclosure envelope. A quotation or technical discussion should clearly identify which elements remain subject to final mechanical confirmation.

Should I choose the cell chemistry before contacting a manufacturer?

You can state a preferred chemistry, but also explain why: space, current, runtime, charging, operating temperature, or existing system compatibility. This lets the engineering review test whether the preference fits the complete application.

What is the minimum information needed for a custom lithium battery pack quote?

At minimum, provide the application, target voltage, runtime or capacity goal, available space, charging approach, target market, expected quantity, and project timing. Current demand and drawings make the response more reliable.

Can one UN 38.3 document cover every battery pack?

Do not assume so. Documentation must be reviewed for the final battery type and configuration, and shipment requirements depend on transport and packing conditions.

The strongest RFQ does not contain the most pages; it contains the right information early enough to guide design decisions. Start with the application and duty cycle, then add electrical limits, integration constraints, BMS and charging needs, market requirements, and commercial context. That gives a custom lithium battery pack manufacturer a basis for a disciplined technical response instead of a generic catalogue reply.

**Have a project brief, drawing, or reference battery?** Send it to Plusenerg for an application-led review. We will identify the missing inputs, confirm what needs validation, and help structure the next battery pack discussion.