In 2021, I participated in a “Builder’s Group” session with my local ham radio club, Williamsburg Amateur Radio Club. We had made portable 12V 100Ah Lithium Iron Phosphate (LiFePo4 or LFP) batteries from Fortune 3.2V 100Ah cells and a separate 120A Battery Management System (BMS). The end product was a portable 1280 watt-hour battery pack.
I configured mine differently because I installed it in my car. See the original entry here. Its capacity tested very well at first, but declined with each passing year. I was able to find small “cheats” that would improve capacity a little, but the practices were not realistic to sustain because they only helped the load test and not real-world use.
This year’s capacity test returned just 74Ah. My JBD BMS has just 100 milliamps of passive cell balancing, which is not nearly enough for a battery that’s charged only when the car is being driven. I decided to experiment with a different BMS in 2025. The new BMS is by JK and features 2-amperes of active balancing. The JK is much more aggressive and successful at balancing my cells.
However, one cell still reaches “low voltage disconnect” (LVD) before the others. The same cell is usually first to reach “high voltage disconnect” (HVD) when the battery is charged from a relatively deep discharge, too. It’s safe to say that one cell has degraded to a point that’s unlikely to be recovered. Continue reading →