It’s not the individual you’re talking about, but this guy will replace batteries. He is an RC car enthusiast and mainly does transponders for those, but he will do the Tranx-160’s that we use in karting. He did one of the older squared off transponders for me a couple of years ago and it’s working great. He runs a HVAC business and doesn’t do a lot of these during his peak busy seasons, but contact him from this page and he will tell you if/when he can do yours.
http://www.krcproducts.com/main_pages/services.htm#AMBrc%20TRANSPONDER%20CELL%20REPLACEMENT