Did you try the Local battery doctor, or battery depot or whatever they call themselves in your town? most can cross referance the P/N and get you an identical unit or rebuild your current unit, may be worth a try unless you have to have a certified one. ( sorry still learning alot here )
Upon further discussion it appears this is likely Artex's strategy to get people to buy new 406 ELTs. Last time they did this with their batteries it was reported to have lasted 6-months.
Silly really...they are just C-sized batteries. In fact MERL said they can rebuild the battery pack for, uh, only $200.
Another tid-bit I learned from talking with folks is that they've had a bunch of troubles with the GPS aided versions... So much that MERL is working on certifying their own that has an integral GPS receiver so as to not rely on a signal from an external GPS.