What causes batteries to burst/corrode while in an appliance?

We've all had an old toy or flashlight or something that when we opened the battery door, saw that it was full of a burst battery and its corroded "acid."





What causes a battery to burst while in an old toy or appliance?|||Most batteries are fine until they go completely dead. Then they corrode and leak.The chemical balance changes when the batteries go dead and the chemicals then attack the metal case of the battery. They don't burst per se, they just rot through the case and the material leaks out. It does kind of look like they burst. The answer is to remove any batteries from any device you're not going to use for a while. If you put a flashlight in a drawer and don't look at it for a year, the batteries could have died and then leaked. Always remove the batteries. Put them in a plastic bag next to the device if you want to make sure that there are batteries handy if you need to use what ever it is. You can see if they've leaked just by looking at the bag.