Lipo batteries are wonderful things and have significantly changed the hobby of flying RC model aircraft. However, they need to be stored safely if you are to avoid a tragedy. My solution to safe lipo storage is to use a large concrete block placed away from flammable materials or objects, preferably on a concrete floor.
In the event that a battery does fail and vent flames, the concrete block will help contain those flames and hopefully avoid a larger fire occurring.
It is also a good idea not to store your batteries in a fully-charged state. Not only does this increase the chances of a fire but, if you store them with 3.8V per cell of charge, they will also last a lot longer.
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