29 Sep '13, 11am
Upgrading Cordless Drill Batteries to Lithium
I did this once, but keeping an eye on the voltage became too much of a hassle. You really need some kind of cut-off circuit that cuts the power when the battery voltage goes low, the voltage drops quickly near the end. The cheap commercial low voltage alarms for RC toys could be a solution, but they draw a lot of power when turned on so they can’t be left plugged in like a normal protection circuit. Normal generic laptop protection circuits might also be used, but you would need to beef up the cut-off transistors since the built in ones wouldn’t handle the starting current of a cordless drill, also the overcurrent protection would have to be removed or it would trip every time the drill started.