Interestingly I'd found using the battery charger @user113488 has made worked pretty well on some older AAA and AA batteries. I tried moving to a newer Ikea battery charger and it just wouldn't touch them, but this one at least gets them to a usable (if not great) charge.
I think being able to force a bit more current into them would really help to put a bit more life into them though
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@allObjects actually a really nice addition would be to stick on the DRV3388 motor driver than you mentioned in another thread (http://forum.espruino.com/conversations/349688) and then also measure the voltage across a resistor.
Interestingly I'd found using the battery charger @user113488 has made worked pretty well on some older AAA and AA batteries. I tried moving to a newer Ikea battery charger and it just wouldn't touch them, but this one at least gets them to a usable (if not great) charge.
I think being able to force a bit more current into them would really help to put a bit more life into them though