You only need 1 battery and they usually last 5 years or longer. You can pick these 2032 batteries up just about anywhere, they are used in many different electronic devices, desktop computers, remotes, calculators, older LCD organizers, and some christmas decorations that are battery operated. Pretty much all stores that sell batteries with an electronics department or a photo department would have these, as well as some drug stores have these mixed in with the hearing aid battery rack, even though I have yet to see a hearing aid take one of these large batteries. There is even a family dollar out by me that sells a 2 pack of these for $1. I picked up a pack of 2 and probably would never need to use them.
No need to buy 5 of these!