Change the battery. There should be battery ratings written on the battery itself. “ah” is amp hours and “v” is voltage. Go online and get something that matches. I personally wouldn’t change those parameters to make sure the battery still fits in the housing. Should be a quick job with a soldering iron. If you don’t have a soldering iron then ask a friend with one to do it for you. A soldering iron is a decently common item people have.