I NEVER had to recharge my lithium+HV drill at all.
Seriously? I hadn't bothered making an MV or HV drill, figuring that they'd have increased power consumption to match the increased battery capacity, and an LV drill didn't make sense to use without some backup power (I'm currently using a charging lapotron crystal), given that it would run out of power faster than a GT diamond pickaxe would run out of durability.