Custom Lithium Battery Pack Design
Quick answer: Custom lithium battery pack design starts from your load profile and mechanical envelope, not from a catalogue. CMX Battery designs packs from cell level up — cell selection and matching, series/parallel architecture, BMS with in-house firmware, thermal path and enclosure — then validates the design with prototypes built on the production line. Send a specification, a drawing, or a duty cycle and we return a design with test data and a certification path.
What “custom pack design” actually involves
A battery pack is a system, and the five subsystems that make it up are tightly coupled. Change the cell and the thermal design changes. Change the series count and the BMS changes. Change the enclosure and the cell layout changes. Designing them in sequence — the way most first-time buyers expect — produces a pack that works on paper and fails in validation.
We design them in parallel. Cell chemistry is selected against duty cycle and temperature range, the electrical architecture resolves series/parallel count against your voltage and current targets, the BMS is specified for your host system’s protocol, and the mechanical design resolves cell layout, thermal path and ingress protection as one problem. The output is a pack that has already been checked against the constraints that cause redesign.
The five design decisions
1 · Cell selection and matching
Cell choice sets the ceiling on everything else. LiFePO4 prismatic cells are our default for stationary and motive applications — flat discharge curve, 3,000 to 6,000 cycles at 80% depth of discharge, and thermal stability that simplifies the safety case. Cylindrical cells in 18650, 21700 and 32700 formats suit serviceable designs and applications where mature supply matters. Large-format prismatic cells up to 314 Ah reduce part count and interconnect resistance in big stationary packs.
Matching matters more than most buyers realise. Cells within a batch vary in capacity and internal resistance; assembled into a series string without matching, that variation compounds into imbalance that the BMS must dissipate as heat on every cycle. We capacity- and IR-match cells per batch before assembly, which is why our packs hold balance where unmatched packs drift within a few hundred cycles.
2 · Electrical architecture
Series/parallel configuration is set by your voltage window and current demand. Our production range covers 12 V, 24 V, 36 V, 48 V, 72 V and 80 V for motive and low-voltage stationary systems, and 200 V to 1000 V+ architectures for commercial and industrial storage, where higher voltage reduces current and therefore resistive loss and cable cost.
Capacity is sized against your load profile rather than quoted as a nameplate figure. A 100 Ah pack delivers 100 Ah at a specified rate and temperature — at 2C continuous, or at −10 °C, usable capacity is lower. We state the derated number up front so your runtime calculation is based on what the pack will actually deliver.
3 · BMS and firmware
The BMS is where OEM differentiation lives. We develop 4S to 16S+ smart BMS designs with in-house firmware, so protection thresholds, balancing strategy, state-of-charge algorithms, low-temperature charge behaviour and fault handling are tunable rather than fixed.
Communications are specified to your host: CAN (including CANopen and J1939 profiles), Modbus over RS485, Bluetooth for service diagnostics, and UART for simple integrations. Give us the protocol specification or the existing communication matrix during discovery and we will match it — protocol mismatch discovered late is one of the most expensive integration failures to fix.
4 · Thermal management
Thermal design is not about keeping cells cool in absolute terms; it is about keeping them uniform. Temperature spread across a pack drives differential ageing, and differential ageing is what ends cycle life prematurely.
- Passive cooling — conduction to the enclosure and natural convection. Lowest cost, silent, no maintenance. Suitable for low-rate stationary and residential storage.
- Forced air — fan-driven airflow across the cell array. Handles moderate continuous load. Adds a service item and an acoustic consideration.
- Liquid cooling — cold plate or dielectric immersion. Specified for high-rate commercial storage and fast-charge applications where cell temperature spread is the binding constraint on cycle life.
5 · Enclosure and mechanical integration
Format follows application: wall-mounted for residential, 19-inch rack for telecom and UPS, floor-standing cabinet for commercial and industrial, containerised for grid-scale. IP65 is standard for outdoor and industrial units. Where the pack drops into an existing product, we work to your mechanical drawing and resolve internal layout around your constraints.
Design parameters we work to
| Parameter | Typical range | Notes |
|---|---|---|
| Nominal voltage | 12 V – 1000 V+ | Common: 12 / 24 / 36 / 48 / 72 / 80 V; 200–1000 V+ for C&I |
| Capacity | 50 Ah – 600 Ah | Per module; parallel for higher |
| Energy (stationary) | 2 kWh – multi-MWh | Cabinet to containerised |
| Continuous current | 0.5C – 3C | Duty-cycle dependent |
| Peak current | Up to 5C short duration | Limited by cell and interconnect |
| Cycle life (LFP) | 3,000 – 6,000 cycles | At 80% DoD, 25 °C |
| Operating temperature | −20 °C to 60 °C | Charge limited below 0 °C |
| Ingress protection | Up to IP65 | Outdoor and industrial standard |
| Communications | CAN / RS485 / Bluetooth / UART | Firmware developed in-house |
From enquiry to validated design
The design stage runs in defined gates so you always know what has been decided and what is still open.
- Requirements capture — load profile, envelope, environment, certification target, volume.
- Feasibility — we confirm the requirement is achievable and flag constraints before quoting.
- Concept design — cell layout, electrical architecture, thermal strategy, preliminary enclosure.
- Detailed design — schematic, BMS logic, mechanical drawings, thermal simulation, bill of materials.
- Prototype build — on the production line, with production tooling and processes.
- Validation — electrical, thermal, environmental and protection testing with recorded data.
- Design freeze — signed off against test data before any tooling or certification spend.
Everything in the design stage is NDA-protected, and designs developed for a customer are not offered elsewhere.
Related routes
- OEM & ODM manufacturing overview — capabilities, process and how programmes run
- Private label — if a validated platform fits your timeline better than a clean-sheet design
- Full process and timeline — stage-by-stage deliverables
- Request a design review — send a specification or a drawing
Frequently asked questions
Can you design to an existing mechanical envelope?
Yes. Send the drawing or the 3D model and we will resolve the internal layout — cell format, series/parallel count, BMS placement and thermal path — within your constraint. If the envelope cannot accommodate the energy target, we will tell you at feasibility rather than after tooling.
How much does custom pack design cost?
Design work is quoted per project. Programmes based on an existing platform carry little or no design cost. Clean-sheet designs involving new tooling and certification carry engineering charges that are usually amortised into unit price against volume. We quote design, tooling and unit price together so the trade-off is visible.
What is the difference between designing for LiFePO4 and NMC?
LiFePO4 has a flatter discharge curve, longer cycle life and better thermal stability, which simplifies the safety case and suits stationary and motive applications. NMC offers higher energy density for the same volume, which matters when space or weight is the constraint. The choice affects cell layout, thermal design and BMS thresholds, so it is decided first.
Do you simulate thermal behaviour before building?
Yes. Thermal simulation is part of detailed design for any pack with meaningful continuous load, and it drives the choice between passive, forced-air and liquid cooling. Simulation is validated against prototype measurements, not accepted on its own.
Can you integrate with our existing inverter or charger?
In most cases yes. Provide the communication specification and we will match the protocol. Where a closed protocol is involved, we can work from a communication matrix or from captured bus traffic. This is resolved during discovery, not during integration.
What happens if the design fails validation?
We iterate. Prototypes are built to be tested and changed, and validation failures are normal in custom work — they are how the design converges. What matters is that validation happens before tooling and certification spend, which is why nothing is frozen until test data is signed off.
Design mistakes we see repeatedly
Most custom programmes that run into trouble fail in one of a handful of predictable ways. Knowing them in advance is cheaper than discovering them in validation.
Sizing to nameplate instead of duty cycle
A pack specified as “100 Ah” because the load calculation arrived at 100 Ah will underdeliver if the load is high-rate or the environment is cold. Capacity is a function of discharge rate and temperature, and the derating is not small — it is common to see 15–25% less usable capacity at high rate or low temperature. Size against the actual profile and the actual ambient range.
Treating thermal design as a finishing step
Thermal behaviour is set by cell layout, interconnect and enclosure, all of which are fixed long before anyone thinks about cooling. A pack layout that traps heat in the centre of the array cannot be rescued by adding a fan later. Thermal strategy belongs in concept design.
Specifying the BMS last
The BMS determines protection thresholds, balancing behaviour and the protocol your host system sees. Specified last, it is chosen to fit decisions already made, and integration problems surface when the pack is already built. Specify it alongside the electrical architecture.
Discovering certification requirements after tooling
Standards such as UL 9540A or IEC 62619 impose design consequences — creepage and clearance distances, enclosure behaviour under thermal runaway, documentation depth. Discovered after tooling, meeting them means redesign. Identify the target market’s standards during feasibility.
What we need from you to start
More detail produces a tighter design, but you do not need a complete specification to begin. In rough order of usefulness:
- Load profile — peak and continuous current, duty cycle, daily throughput. More useful than a capacity figure.
- Voltage window — nominal system voltage and acceptable operating range.
- Mechanical envelope — dimensions, mounting, weight limit, or an existing drawing.
- Environment — ambient temperature range, indoor or outdoor, ingress requirement.
- Target certification — market and applicable standards.
- Volume — annual quantity and expected ramp. This drives tooling decisions.
If you have a problem description rather than a specification, that is a workable starting point. Describe what the battery has to do and what it has to fit into, and we will work backwards to a design.