I was sick and tired of my kids leaving their battery power toys left on and draining the batteries. Especially the toy walkie-talkies which use a 9V battery that are more expensive to replace.
So I added a small circuit to disconnect the battery when it had not been used for some time. A push button is needed to turn it on and start the timer. The walkie-talkies already had one so I just stole this.
For reference here is a typical schematic for a kids walkie-talkie.
Looking around on the net I found these other battery saver circuits