Ok. So, obviously, literally, if you have a battery (电池) 充电 does mean to charge it, but that's as far as the metaphor goes.
The english (charge or recharge one's batteries) is not related 充电。
充电 = to brush up on, study up on something
from the chinadaily bbs, (yes, I know)
Seems about right to me. To go review something.