What to know in 60 seconds
If you need a tailored power solution, a custom LiFePO4 battery pack design (small series-parallel configuration) gives the best balance of voltage, capacity and form factor. This guide explains the core design choices, the BMS features you must specify, the acceptance tests to require, and a short RFP checklist you can copy into supplier requests.
Table of contents
- Why choose a custom pack (quick business case)
- Series vs parallel — the core tradeoffs
- 7 critical design rules for reliable packs
- BMS features you must demand (and why)
- Acceptance tests & sample plan (what to put in an RFP)
- Real example: Himax 12.8V 42Ah 4S2P pack (spec + lessons)
- FAQ (schema-ready) + Next steps & CTA
1. Why choose a custom pack? (short business case)
Off-the-shelf modules are fast, but for size, thermal behavior, or interface requirements you often need a custom LiFePO4 battery pack design. Benefits for OEMs and integrators include:
· Tailored voltage and capacity to match system electronics
· Optimized BMS and communication (CAN / Modbus, etc.)
· Better packaging/thermal layout that increases cycle life and reliability
A smart custom design reduces total cost of ownership — not just the unit price.
2. Series vs parallel — the core tradeoffs
· Series (↑ Voltage): increases pack voltage; keep cell voltages tightly matched.
· Parallel (↑ Capacity): increases Ah and current capability; more cells → greater mechanical/thermal complexity.
· Small series-parallel (e.g., 4S2P) is common for compact industrial packs — it balances ease of assembly and serviceability.
When planning a custom LiFePO4 battery pack design, choose the smallest number of parallel strings that meet current requirements to reduce balancing load and manufacturing variability.
3. Seven critical design rules for reliable packs
1. Cell matching & batch traceability: use cells from the same production lot and document lot IDs.
2. Design for balancing: passive balancing may be fine for small packs; use active balancing for high-cycle applications.
3. Robust mechanical layout: avoid cell stress; add vibration damping for mobile devices.
4. Thermal path & sensors: place temperature sensors near the hottest cell groups and provide a clear thermal dissipation path.
5. Redundant safety devices: fuses, current sensing, and MOSFETs sized with margin.
6. Accessible service points: make BMS diagnostics ports reachable for field servicing.
7. Documented test plan: acceptance criteria must be measurable (capacity % tolerance, IR limits, BMS alarm thresholds).
These rules should be codified in your RFP for any custom LiFePO4 battery pack design tender.
4. BMS features you must demand (and why)
A well-specified BMS is the difference between a safe pack and a field headache. For custom series-parallel packs insist on:
· Per-cell voltage monitoring & balancing (report logs)
· MOSFET failure detection & fail-safe cut-off
· Over/under voltage thresholds and configurable hysteresis
· Temperature monitoring with defined placement and alarm actions
· Communication: CAN / RS485 / Modbus (if your system needs telemetry)
· Event logging (so you can audit failures and warranty claims)
Ask suppliers to include a BMS behavior matrix in proposals — it should state exact thresholds, response times, and communications frames.
5. Acceptance tests & sample plan — copy-paste into your RFP
Require these tests on the supplied sample batch (30–90 day test window):
Electrical
· Capacity test at specified C-rate (e.g., 0.5C discharge to cutoff) — report Ah and % of rated capacity.
· Internal resistance (IR) sampling across N random cells.
· High current pulse test to validate voltage sag and thermal response.
BMS & Safety
· Simulated cell short and MOSFET failure test with logs.
· Overcharge / overdischarge protection tests.
· Temperature abuse snapshots (within safe lab limits).
Mechanical & Environmental
· Vibration + shock sample (if application is mobile).
· IP rating verification if intended for outdoor use.
Acceptance criteria (example):
· Capacity ≥ 98% of rated on sample run.
· IR per cell within ±10% of sample mean.
· No BMS fatal event in 7 days of cycling tests.
Including a clear acceptance test plan cuts months off qualification time.
6. Real example: Himax 12.8V 42Ah (4S2P) — brief specs & learnings
· Config: 4S2P (12.8V nominal), 42Ah
· BMS: CANBus telemetry, MOSFET failure alarm, passive balancing
· Thermal design: integrated heat spreader + two temperature sensors
· Result: 25% longer runtime in robotic application vs off-the-shelf module; predictable degradation profile.
Lesson: early co-design (engineer + Himax) reduced rework and sped up mass production.
UN 38.3 transport test requirements
7. FAQ (short) — publish these as page FAQ for users & search
Q: How long does it take to prototype a custom small series-parallel pack?
A: Typically 3–6 weeks for prototype + 4–8 weeks for sample testing depending on the acceptance plan.
Q: What is the minimum order quantity (MOQ) for custom packs?
A: MOQs vary, but many custom runs can be structured with a small pilot order followed by scalable production.
Q: Do you provide BMS firmware customization?
A: Yes — we offer BMS firmware tuning, CAN/Modbus integration, and diagnostic logging features.
Next steps — RFP snippet & CTA
Copy this RFP field list into supplier requests: pack voltage/Ah, maximum continuous current, required BMS features, sample qty & test plan, certifications required (UN38.3, IEC62619), lead time expectations, warranty.
Get started: Contact Himax Battery Engineering to request a free feasibility review for your custom LiFePO4 battery pack design.
