Agree that the preferred option is a new unit.
Still, I can't help feeling like the whole thing is a bit of a scam. I understand that inspected commercial vessels need a certified EPIRB and re-certifying the replacement battery installation is a highly specialized field. Fine.
But as a recreational boater, I often wonder whether I could find batteries to match the original spec and "self-certify." That is to say, verify that I put it back together correctly and it's still waterproof. For recreational, coastal boating this is a tertiary backup at best. I already have fixed and hand-held VHF radios, cell phones, an InReach and PLB. Sure, I'd like to be sure my EPIRB works, but I don't need to pay someone hundreds of dollars to verify that.