9 Volt batteries are good for a lot of things, but they are also somewhat dangerous as both terminals are on the same side and if they are not stored right can create a spark or heat up to the point where they could start a fire. Actually we share a tutorial on how to use a 9 volt battery to start a fire when shooting steel wool sparkles.
The folks at hdslrnow sent us this quick tip about using a pill case to store a 9V battery so the terminals are protected.
And here is a reminder on why you really (really) want to protect the terminals. It can burn your house.