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BLUS ENERGY
Manufacturing2026-06-08 · 10 min read

Custom Lithium Battery Pack Design: An OEM/ODM Guide from Requirements to Mass Production

What actually happens between “we need a custom battery” and a certified pack rolling off the line — cell selection, BMS, certification, timeline and the decisions that make or break a project.

DC
Written by Daniel Chen
Senior Battery Systems Engineer · BLUS ENERGY R&D
Technically reviewed by BLUS ENERGY R&D Team
Automated lithium battery pack assembly line at the BLUS ENERGY factory
Off-the-shelf batteries are convenient until your product needs a specific voltage, footprint, connector, run-time or certification. That's when an OEM/ODM custom pack makes sense. This guide maps the full journey — from a one-line requirement to a certified pack in mass production — so you know what to prepare and where projects succeed or stall.

The NPI workflow at a glance

From requirements to mass production
1. Requirementsvoltage · capacity · size · certs2. Design & DFMcell pick · BMS · 3D layout3. PrototypeA-sample · bench test4. QualificationUN38.3 · IEC62133 · abuse5. Tooling & Pilotfixtures · process FMEA6. Mass Production100% QC · traceability
A typical new-product-introduction (NPI) flow. With pre-validated cells and modular BMS, the first prototype is often 4–6 weeks out.

1. Nail the requirements first

The fastest projects start with a clear spec. Bring: nominal voltage and capacity (or run-time at a given load), peak and continuous current, physical envelope and weight limit, connector/pinout, operating temperature range, target certifications, and expected annual volume. Each one shapes the cell choice and BMS.

2. Cell selection and configuration

First the chemistry (see our LFP vs NMC comparison), then the format — pouch/polymer for thin custom shapes, cylindrical (18650/21700) for rugged high-cycle packs. Cells are then arranged in series (S, raises voltage) and parallel (P, raises capacity and current). A “10S4P” pack, for example, is ten cells in series, four such strings in parallel.

3. BMS: the intelligent core

The BMS continuously tracks voltage, current and temperature; protects against over-charge, over-discharge and short circuit; balances cells; and reports State of Charge and health. Match its continuous/peak current to the load, and choose the communication bus your system needs — I²C, UART, SMBus or CAN for smart packs that talk to a host or inverter.

4. Certification — plan it from day one

Certification is not a final step you bolt on; it constrains the design. UN38.3 is required to ship lithium batteries by air and most sea/road freight. Product-safety standards such as IEC 62133 depend on the market and application:
Common certifications by purpose
StandardPurpose / scope
UN38.3Transport safety for lithium cells & batteries (air/sea/road)
IEC62133Safety of portable sealed secondary cells/batteries
UL2054 / UL1642North-America household & commercial battery safety
IEC62619 / UL1973Industrial & stationary energy-storage cells
CE / UKCAEU / UK market conformity
KC · PSE · BISKorea · Japan · India market access

5. Timeline, tooling and cost

Expect roughly 4–6 weeks to a first prototype with pre-validated cells, then qualification and a pilot run before mass production. Custom projects carry non-recurring engineering (NRE) and tooling costs up front; for products shipping in volume, a custom pack typically pays back within the first or second production year through better fit, performance and unit cost.
See the production floorWatch our cell assembly & QC line on YouTube

Choosing a manufacturing partner

  • In-house cell, BMS and pack engineering — not just assembly.
  • A documented qualification process (UN38.3 / IEC62133) with real reports.
  • Traceability and 100% end-of-line testing in mass production.
  • Willingness to engineer to your load profile and own the NPI journey with you.
BLUS ENERGY runs the full path in-house — from cell selection and BMS to certification and mass production — across polymer, cylindrical and LiFePO4 platforms. Tell us your requirements on the contact page and an engineer will reply within 24 hours.

Frequently asked questions

How long does a custom battery pack take?+

With pre-validated cells and a modular BMS, a first prototype is typically 4–6 weeks out. Full qualification (including UN38.3) and a pilot run follow before mass production.

What information do you need to quote a custom pack?+

Nominal voltage and capacity (or run-time at a load), peak/continuous current, size and weight limits, connector, operating temperature range, target certifications and annual volume. A load profile is the most useful single input.

Which certifications does a lithium battery need?+

UN38.3 for transport is almost always required. Product safety depends on market and use — commonly IEC62133, UL2054 or UL1642 for portable, IEC62619/UL1973 for stationary storage, plus CE/UKCA, KC, PSE or BIS for specific regions.

Is a custom pack worth it versus off-the-shelf?+

For products shipping in volume, usually yes — a custom pack fits the exact envelope, hits the required run-time and certifications, and typically pays back its NRE/tooling within the first or second production year through better unit economics.

Keep reading

Lithium cell formation line where LiFePO4 and NMC cells are conditioned and gradedLiFePO4 vs NMC Lithium Batteries: A Practical Engineering Comparison (2026)9 min read12V 100Ah LiFePO4 batteries installed in a residential energy-storage setupHow to Choose a 12V 100Ah LiFePO4 Battery: A Buyer's Guide That Goes Beyond Capacity8 min read

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