Designing a custom battery pack involves far more decisions than most OEM teams expect at the start of a project:
Whether it is a medical device, an industrial sensor, or a defense platform, missing even one step in the design process can delay a launch or create a safety issue down the line. Most engineering teams benefit from a clear, structured checklist before committing to a design. As custom power requirements grow more complex in 2025 and 2026, having a repeatable process has become essential for OEMs building battery-powered products. The full process comes down to:
Cell selection, BMS design, mechanical engineering, and certification, working together as one system.
Step 1: Define the Application Requirements
Before any design work begins, the pack’s real-world requirements need to be locked in, including:
Skipping this step is the most common reason custom battery projects run into rework later.
Step 2: Select the Right Cell Chemistry
Different chemistries offer different tradeoffs in energy density, safety, and cost. Common options include:
The right choice depends entirely on the application’s power, weight, and safety requirements.
Step 3: Design the Battery Management System
A properly engineered BMS is what keeps a custom pack safe and reliable throughout its lifespan. Key BMS design considerations include:
Step 4: Engineer the Mechanical Enclosure
The enclosure protects the cells and electronics while fitting the constraints of the final product. Enclosure design should account for:
Step 5: Plan for Manufacturing and Assembly
A design that looks good on paper still needs to be manufacturable at scale. This step should confirm:
Step 6: Build In Regulatory and Safety Compliance
Certification requirements should be considered early, not added at the end of the project. Common requirements include:
Step 7: Test, Validate, and Iterate
Before finalizing a design, packs should go through rigorous testing, including:
Test Type | What It Confirms |
Thermal cycling | Performance across temperature extremes |
Vibration and shock testing | Durability in real-world conditions |
Charge and discharge cycling | Long-term capacity retention |
UN38.3 transportation testing | Safety for shipping and logistics |
BMS functional testing | Accurate protection and monitoring behavior |
Step 8: Plan for Charging Compatibility
A custom battery pack is only as reliable as the charger paired with it. This step should confirm:
Step 9: Plan for Scalability and Future Revisions
A custom battery pack rarely stays static after launch. Products evolve, regulations change, and supply chains shift. Building flexibility into the design from the start helps avoid costly redesigns later, including:
Even well-resourced engineering teams run into avoidable problems during custom battery pack development. Common pitfalls include:
Cost decisions made early in a custom battery pack project often have the biggest long-term impact. Teams should weigh:
Balancing these factors early helps avoid both overspending on unnecessary features and underspending in ways that create risk later.
Custom battery pack design touches multiple disciplines at once, and the strongest results come from close collaboration between:
Projects that treat these disciplines as separate, sequential steps tend to experience more delays than projects that involve all stakeholders from the earliest planning stages.
The requirements phase often gets rushed because it does not involve visible design work, but it has the biggest impact on how smoothly the rest of the project goes. A thorough requirements phase should also capture:
Teams that document these requirements in writing before design work begins tend to move through later stages with far fewer surprises.
Once chemistry is selected, OEMs also need to decide between standard cell counts and configurations versus a fully custom arrangement. This decision affects cost, lead time, and flexibility:
Following this checklist internally is useful, but most OEMs still rely on an experienced manufacturing partner to execute it. When evaluating a potential partner, look for evidence that they can support the full process, not just one piece of it:
A partner who can speak confidently to every step of this checklist, rather than just cell sourcing or assembly, is far more likely to deliver a pack that performs reliably and meets certification requirements on schedule.
Custom battery pack design touches electrical engineering, mechanical design, manufacturing, and regulatory compliance all at once. OEMs that partner with an experienced custom battery pack manufacturer benefit from:
Medical Devices
Patient safety depends on precise, validated, and certified battery performance.
Drones and UAVs
Weight, thermal, and BMS tuning directly affect flight time and reliability.
Defense and Military
Mission-critical equipment requires rugged design and strict compliance.
Industrial IoT
Long field deployments demand consistent, long-lasting battery performance.
How long does custom battery pack design typically take?
Timelines vary by complexity, but most custom projects move through requirements, design, prototyping, and certification over several months.
Do I need to choose a BMS before designing the enclosure?
Yes. BMS placement and thermal behavior directly affect enclosure size and design, so these steps should happen together.
What certification is required for shipping lithium battery packs?
Most lithium battery packs require UN38.3 transportation safety testing before they can be shipped by air or sea.
Can an existing off-the-shelf pack be customized instead of designed from scratch?
In some cases, yes, but applications with unique size, safety, or performance requirements usually benefit from a fully custom design.
Who should be involved in the battery pack design process?
Electrical engineers, mechanical designers, and compliance specialists should all be involved from the early requirements stage through final testing.
What is the biggest cause of delays in custom battery pack projects?
Finalizing the enclosure or certification plan before the BMS and cell configuration are locked in is one of the most common causes of costly, time-consuming redesigns.
How much prototyping should be expected before production?
Most custom projects go through multiple prototype iterations to validate performance, thermal behavior, and certification requirements before committing to full production.
Does the checklist change for non-rechargeable battery packs?
Some steps, such as BMS design, may be simplified or unnecessary for non-rechargeable packs, but cell selection, enclosure design, and certification remain essential.
How often should a custom battery pack design be revisited after launch?
Design reviews are recommended whenever cell suppliers, regulations, or product requirements change, even if the pack has already passed certification.
A successful custom battery pack design depends on treating cell selection, BMS design, enclosure engineering, and certification as one connected process rather than separate steps. OEMs that follow a structured checklist reduce risk, avoid costly rework, and bring safer, more reliable products to market.
Explore Emerging Power’s custom battery design services or learn more about our compliance and regulatory capabilities to build a pack that meets every requirement from day one.
