Battery Tester

Lithium-ion 18650 cells are commonly found in old laptop batteries, so you can often get them for free at recycling stations. But older cells can be degraded, so I built a battery tester that measures cell health.

Up to 10 cells can be placed on the loading side. The machine feeds one cell at a time, discharges it, charges it back up, logs capacity and internal resistance, then loads the next cell automatically.

Bad cells were discarded. The good ones were arranged into a pack based on each cell's remaining capacity.

Each cell can also be inspected in detail. This graph shows energy vs. voltage (blue) and internal resistance vs. voltage (green).

I used the good cells to build an electric longboard. I coded a phone app as the throttle, sending the signal to a Bluetooth module on the board.

It looks like shit, but it taught me the basics of electronics, soldering, app development, and Arduino. I used it to commute to work for one summer.