At the conclusion of our webinar, Custom Battery Pack Design Considerations for Performance and Safety, we had several questions submitted to our presenter, Battery Product Manager Anton Beck. We compiled these into a readable format on our blog.
Q&A From Our Live Webinar
Quick Links:
- How do you know what type of cell to select for your project?
- How do you determine when the battery should be charged if it's not being used or has been in long-term storage?
- How do you determine what type of material will be required for an enclosure?
- How do you plan for controlling thermals in the battery enclosure?
- Can Epec certify battery packs for other customers or companies?
- Do all battery packs need a BMS to control the charge and discharging?
- Can resettable fuses be used in packs?
- Is EMI/RFI shielding needed for battery packs?
- What are the development costs, including certifications, for the case study #2 battery? (Just a ballpark number as a guideline).
Watch the Recording Below:
Question: How do you know what type of cell to select for your project?
Answer: You have to determine how much capacity and voltage your device is going to require, including what the device will draw in current. Different types of cells have different capacities and discharge rates. So, cell form factor will need to be considered, so you can design a pack within the dimensional space constraints you have.
Question: How do you determine when the battery should be charged if it's not being used or has been in long-term storage?
Answer: The answer to that would be that all chemistry is really self-discharge, and the BMS on the battery is going to typically draw some milliamps. So, the rule of thumb is to charge batteries when you receive them if you can. If you have to store it long-term, keep the batteries at approximately 50% state of charge. Check them every six months to verify voltage levels, and charge again if required.
Question: How do you determine what type of material will be required for an enclosure?
Answer: There are many options, such as polycarbonates and ABS, aluminum, etc. It all varies depending on environmental conditions, the weight of the battery pack, and aesthetics. So, you know, you have to work with your marketing team as well, as far as how you want that enclosure to look, and factor in how heavy the battery is going to be, etc.
Question: How do you plan for controlling thermals in the battery enclosure?
Answer: So, the design of the enclosure should allow for heat to dissipate somehow, by having some spacing in the enclosure, maybe spacing between the cells if you can manage it. It could be designed with vents if the application allows, if it's not IP-rated. Some advanced thermal interface materials help dissipate the heat away from the battery. And some enclosure designs even incorporate cooling fans if the battery is anticipated to get hot during charge and discharge cycles. There are a lot of options, actually.
Question: Can Epec certify battery packs for other customers or companies?
Answer: The answer is no. We don't do that. Epec only certifies the batteries we design because the certification process is based on how the electrical system is created, as well as the enclosure. Certifying after the battery is already designed and locked in poses a risk of failure if the design requirements haven't been met. So, we only certify the batteries we design and support.
Question: Do all battery packs need a BMS to control the charge and discharging?
Answer: The BMS is mainly for lithium batteries, but we have some nickel battery designs, like metal hydride, that use a BMS. And you've got to keep in mind that all lithium battery packs require safety protection as a minimum to be able to pass UN38.3. So, not all battery packs require BMS, but lithium, to manage and get the most out of life cycles, it's definitely required.
Question: Can resettable fuses be used in packs?
Answer: Yes, resettable fuses can be used in packs, but usually only for low-current packs or as secondary safety layers.
Question: Is EMI/RFI shielding needed for battery packs?
Answer: For simple packs (cells and basic protection) EMI/RFI shielding is usually not needed. For smart packs (with BMS, comms, DC-DC converters, or high switching currents), shielding may be necessary, depending on regulatory requirements and the sensitivity of the end device.
Question: What are the development costs, including certifications, for the case study #2 battery? (Just a ballpark number as a guideline).
Answer: The development costs for that battery were approximately $125,000 to include the BMS development, enclosure design and tooling, samples required for UN38.3 and UL2054, and the certification testing. This battery was designed, developed, and supported domestically here in the U.S.
Key Takeaways
- Cell selection is driven by application needs: Voltage, current draw, capacity, and physical size all dictate the right cell type. The form factor must fit the available space while meeting electrical performance.
- Long-term storage requires maintenance charging: Because all chemistries self-discharge and the BMS draws current, battery packs should be stored at roughly 50% state of charge and rechecked every six months to avoid deep discharge.
- Thermal control depends on enclosure design: Effective heat management can include venting, internal spacing, thermal interface materials, and even active cooling such as fans, especially for high-current or tightly packed designs.
- Lithium packs require safety circuitry: A BMS is mandatory for lithium batteries to manage charging, discharging, and safety protections needed to pass standards like UN38.3. Some nickel chemistries may also use BMS for enhanced control.
- Certifications only apply to in-house designs: Epec can only certify battery packs they design and build, as certification depends on the complete integration of the electrical system and enclosure from the beginning of development.
