As a father of a young family with toys that require many AA and AAA batteries (some LEGO set require 10 AAA batteries!), I rely on rechargeable batteries for power. The ensure the kids always have acces to fresh batteries I laser-cut the simplest possible rechargeable battery manager imaginable. It has slots for AA, AAA and 18650 LiPo batteries.
In essence it is a number of layers of glued plywood laser cut on the Lasersaur and a simple instruction to the kids: