These aluminum capsules are great for keeping things dry that need to stay dry. Stuff pills, money, tinder, or anything else inside. These have flat bottoms, so you can set them on a table or other surface while loading them up with goodies. There is an o-ring to make it watertight, and a split ring so you can attach it to your keychain, pack, or anywhere else. One AA battery will fit perfectly inside this capsule.
Please note that the pictured battery is not included and is just for size reference.