When we saw [Max.K]’s automatic NiMh battery charger float past in the Hackaday ... it feels like a product rather than a project, and really delivers on the promise of 3D printing.

you should really invest in a charger that is capable of running some capacity tests against the cell. Or if you’re a bit more adventurous, you can build this “Battery Health Monitor ...

Powered by a 6A lithium battery of its own, the 12V smart charger is controlled using a built-in LED display that shows the current, voltage, temperature, battery power, and more in real time.