440 WHr Li-Ion Battery Packs Qualified and Built for Space

In 2021 EPL set out to create a fully containerized propulsion module, the APS 500 (Ammonia Propulsion System), which could provide smallsats with industry leading performance and a great tradeoff between specific impulse and thrust authority. In an effort to minimize SWaP, the APS 500 was designed to run entirely off a battery pack. Thus, EPL designed, built, and fully qualified affordable Li-Ion battery packs for use in the APS 500 and other payloads .

EPL’s Li-Ion battery packs have been extensively ground tested to ensure absolute reliability for critical components in space. The battery packs have been proven in vacuum under load, vibe tested, and life tested.

Prototype APS 500 Propulsion Module with Integrated 440 WHr Li-Ion Battery Pack

Prototype 440 WHr Li-Ion Battery Pack, Vibration Test

Prototype 440 WHr Li-Ion Battery Pack, Life Test

All of EPL’s Li-Ion battery packs use COTS 18650 battery cells which have flight heritage through EPL’s APS 500 and numerous other public missions. To circumvent the harsh radiation environment of space, the battery packs do not use a Battery Management System (BMS). Instead, all battery cells go through a rigorous and discriminatory screening process before battery pack assembly. The screening process ensures that all cells are closely matched and will not contribute to performance issues over the life of the battery pack. Additionally, all battery packs are internally potted to alleviate temperature differences in the battery cells, particularly between inner and outer cells.

EPL has qualified our 440 WHr battery packs to an End-of-Life (80% initial capacity) of 1,500 charge and discharge cycles over the course of a three year in-house life test program. To reach this large amount of discharge cycles, the Depth-of-Charge must be kept to about 95% nominal capacity and the Depth-of-Discharge must be kept to about 35% nominal capacity.