Battery jinki idea

A battery that saps a portion of the user's strength for a period of time, until the user switches the battery on to access the stored strength for a condensed set period by changing the voltage and current.

I haven't thought of limitations/risks other than storage limits and overloading a vessel with energy.

I was thinking of the user as a wanderer who uses the battery for day-to-day usage, and uses it for survival/energy distribution for when he really needs energy.