The Battery is an item in the Kirby games. It has only appeared in two games so far.
Kirby Air Ride
The Battery Patch as seen in City Trial
The Battery appears as a patch in City Trial, and is used to upgrade a machine's charging speed, making it charge faster. A battery with a lightning bolt will make Kirby's air ride machine go out of control. A battery with an "X" on it will make the machine travel at a fixed (slow) speed of 16mph and be unable to charge, so it should be avoided.
In Kirby & the Amazing Mirror
Batteries are found as common items scattered across the Mirror World. They power Kirby's Cell Phone, which uses one battery every time it is used. The phone only can have 3 batteries.