Custom Battery Pack Design Requirements: OEM RFQ Checklist
A useful custom battery pack RFQ should define the application, electrical load, mechanical envelope, BMS and communication needs, charger and connector interfaces, operating environment and validation expectations before the design is frozen. This checklist helps OEM engineering and purchasing teams provide the information a battery supplier actually needs to move from quotation to a workable prototype.
Do not send only voltage and Ah
A custom battery pack is a system integration project. Voltage and capacity are only the starting point. The supplier also needs continuous and peak current, duty cycle, BMS protection logic, communication interface, enclosure constraints, connector and charger requirements, temperature and ingress conditions, target-market documentation, and the test criteria that define an acceptable sample. Providing these inputs early reduces quotation assumptions, late redesign and prototype delays.
12 design inputs to define before a custom battery pack quote
The exact level of detail depends on project maturity. If some items are still open, mark them as assumptions rather than leaving them undefined.
| Requirement | What the OEM should provide | Why the battery supplier needs it |
|---|---|---|
| 1. Application | Equipment type, operating mode, replacement vs new design, expected production use. | Sets the design context, duty cycle, service expectations and application-specific risks. |
| 2. Nominal voltage | Required system voltage and allowable operating voltage window. | Defines cell series count, BMS voltage range, charger voltage and controller compatibility. |
| 3. Capacity / energy | Target Ah or kWh plus required runtime under a defined work cycle. | Determines parallel cell count, energy reserve, weight, size and thermal loading. |
| 4. Continuous current | Normal operating current or power under sustained load. | Drives cell selection, busbar, cable, connector, fuse and thermal design. |
| 5. Peak current | Startup or transient current, duration and repetition frequency. | Helps set BMS over-current logic and prevents nuisance shutdown or undersized power paths. |
| 6. BMS functions | Protection thresholds, balancing, SOC/SOH needs, logging and service diagnostics. | Defines control logic, sensing, data requirements and validation scope. |
| 7. Communication | CAN, RS485, RS232 or other interface; protocol, messages and controller/charger requirements. | Ensures the battery, vehicle/equipment controller and charger exchange the required data. |
| 8. Mechanical envelope | Battery compartment drawing, maximum dimensions, mounting points, removal path and service clearance. | Prevents late enclosure redesign, cable strain, cover interference and poor field serviceability. |
| 9. Connector / harness | Preferred connector, mating direction, cable exit, harness length and equipment-side interface. | Links current capability, service access and equipment integration to the physical battery design. |
| 10. Charger | Charger model or required voltage/current, charge location and communication needs. | Confirms charging compatibility, cutoff behavior, connector arrangement and thermal conditions. |
| 11. Environment / compliance | Temperature, vibration, moisture/dust exposure, destination market and required transport/product documentation. | Defines enclosure, sealing, thermal and validation requirements and the project compliance plan. |
| 12. Prototype acceptance | Required test data, equipment test, sample quantity, validation procedure and approval criteria. | Creates a measurable gate between first sample, pilot build and mass production. |
Voltage, capacity and current must be tied to a real load profile
Battery sizing should start from how the equipment actually operates, not only from a nominal voltage label or an expected Ah number.
Voltage and usable energy
Specify the equipment operating voltage window and the runtime target under a defined work cycle. Energy in watt-hours is approximately nominal voltage × amp-hours, but usable runtime also depends on load profile, BMS limits, temperature and reserve margin.
- Nominal system voltage
- Minimum / maximum acceptable voltage
- Target Ah or kWh
- Expected runtime and work cycle
Continuous and peak current
Peak current is especially important for motors, pumps, compressors, traction systems and other equipment with startup or transient loads. Provide duration and repetition frequency whenever possible.
- Normal continuous current
- Peak current and duration
- Regenerative or reverse current if applicable
- Maximum charging current
Define what the BMS must protect, measure and communicate
BMS requirements should be aligned with the controller, charger and service strategy before the sample is built.
Protection and control logic
Define protection thresholds and any application-specific timing or recovery logic for over-current, over/under-voltage, charge/discharge temperature and other relevant faults.
- Cell and pack voltage protection
- Charge/discharge over-current
- Temperature protection
- Balancing expectations
- SOC / SOH and fault logging needs
CAN, RS485 and system interfaces
If the battery must communicate with an equipment controller, inverter or charger, define the physical interface and data requirements early. For protocol selection, see our CANBus vs RS485 guide.
- Required interface and baud rate
- Controller / charger integration
- Required data points and alarms
- Termination and connector requirements
The battery compartment drawing is one of the most useful RFQ files
Mechanical constraints determine whether the final battery can actually be installed, connected, cooled, removed and serviced safely in the equipment.
For projects where the battery wiring and equipment interface are customized, review our battery wiring harness capabilities and the OEM battery wiring harness design checklist.
Interfaces and operating conditions must be specified before design lock
Connector and wiring harness
Provide the preferred connector family if already fixed, or at least the required current, cable size, mating cycles, sealing level, mounting position and equipment-side connector. Connector selection should be reviewed together with harness routing and service access.
Charger interface
State whether an existing charger must be retained or a new charger can be selected. Include target charge voltage/current, connector arrangement, charge location and any CAN/RS485 handshake requirements.
Operating environment
Define minimum and maximum ambient temperature, moisture/dust exposure, vibration, cleaning chemicals, altitude or other conditions relevant to the equipment.
Compliance scope
Identify destination markets, transport requirements and any project-specific certification or documentation expected. Requirements such as UN38.3, IEC 62619, UL 1973, CE or RoHS depend on the product architecture, application and market; they should be confirmed as project requirements rather than assumed for every pack.
What to send a battery supplier for a faster technical review
A concise, structured RFQ package is more useful than a long email with mixed assumptions. Send the files that define the equipment and clearly mark which values are fixed and which are still open for engineering discussion.
Six reasons custom battery quotes become inaccurate or slow
Use the RFQ to create an engineering baseline, then validate the sample against it
The purpose of the RFQ is not only to get a price. It should create a shared technical baseline for battery architecture, interfaces and acceptance criteria. The next step is prototype validation before any pilot or mass-production release.
Custom battery pack RFQ questions from OEM teams
What information should an OEM provide for a custom battery pack RFQ?
Provide the application, target voltage and capacity, continuous and peak current, duty cycle, BMS and communication requirements, enclosure constraints, connector and charger interface, environmental conditions, target-market compliance scope and sample validation requirements.
Why are continuous and peak current both required?
Continuous current defines sustained electrical and thermal load. Peak current shows startup or transient demand. Both influence cell selection, BMS settings, busbars, cables, connectors, fusing and thermal design.
Should the supplier receive the equipment battery compartment drawing?
Yes. Dimensions, mounting points, cable exit direction, connector access, cooling space and service clearances are important inputs for enclosure and harness design.
When should CAN or RS485 requirements be defined?
Before prototype design lock. Provide controller or charger interface requirements, protocol expectations, termination requirements and the data points that must be exchanged.
What compliance information should be included?
Identify destination markets, transport requirements and any product-specific certification or documentation needed. The exact compliance plan depends on the application, battery architecture and market.
Can an RFQ start before every detail is finalized?
Yes. Start with confirmed requirements and a clearly marked list of open items. Distinguishing fixed requirements from assumptions allows the supplier to manage technical risk without pretending uncertain inputs are final.
Preparing an OEM battery RFQ?
Send your application, voltage, capacity or runtime target, continuous/peak current, battery compartment information, communication requirements, charger/connector details and operating environment. Chalong Fly can review the project inputs and identify the engineering information needed before prototype design.
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