I wanted to design a arduino based battery charger, maybe using the pi zero. The arduino would probably control a 28-30v power supply via pwm, and have inputs for voltage, current, and time limits. It would also have different charge profiles for different battery types (nimh, nicd, lead acid, lipo). Also, have an option for battery capacity testing! Using a pwm load with setting for discharge current and cutoff voltage you just need to measure the hours until cutoff and multiply by load current. A good base power supply would be an old wheelchair battery charger, usually 24V 10A. I am disabled (sma), and have worked on electronics since I was 8 (now 38). Oddly enough my name is also Ben and I live in Austin Minnesota.