Things like discharging too quickly, overcharging, punctures, and internal short circuits can all cause a battery to fail this way. So lithium battery manufacturers add several stages of safety measures to make sure nothing goes wrong. Some have even shot holes through a fully charged battery to make sure it wouldn’t explode.

But there have been a lot of problems in recent years with counterfeit batteries, which look like “proper” batteries from the outside (Dell, Apple, Sony, whatever) but are not made with the same safety measures. If you’re shopping for a battery and you find a price that’s too good to be true, it’s probably too good to be true!

Lithium polymer batteries are about the same as lithium ion batteries as far as safety is concerned. They operate with nearly the same chemistry, but using a gel rather than a liquid. Both types have vents to prevent buildup of excess pressure.