system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come batteries can die out without being used just from placing them in a device, but keep their energy stored if not?
gpt
Lots of devices aren't entirely off. They maintain a clock, volatile memory and such. So if you leave the batteries in there is a slow drain on them that isn't present normally. 

Of course, batteries don't strictly speaking keep their energy when stored. Single use batteries can hold a long time, but rechargeable often leak away their charge in a month or so.