9 volt batteries are useful items to include in your hiking, camping, and survival gear. When touched to a wad of steel wool you have an INSTANT hot starter fire. The thing is, you want to protect those exposed terminals from contact with anything that might short out and drain the battery. This original design cap does just that. The small enclosure on the inside further isolates and protects the positive terminal. Apply a small amount of caulk around the base of the cap and it is totally waterproofed as well. Enjoy! I make these on a 3D CUBE printer using ABS plastic. Print time is about 50 minutes.