This is an extra battery for the 2 heated vests that I have bought for my husband. The older one was bought 3 years ago and he loved it. When it failed a few weeks ago, we didn't know if it was the vest or it's battery. So, I bought him a new vest. We tried the new battery in the old vest and it worked perfectly, I then bought this battery as a spare. My husband suffers fro Raynaud's syndrome and is constantly feeling cold. These vests are first class and make his life so much more comfortable.