my Epirb battery expired a year ago. However, the self-test does still respond positively, giving me a green light which, as I understand it, says the unit is fully operational. However, I do not want to take a chance with the battery while sailing offshore, possibly hundreds of miles off of the coast and evaluated my options. Replacing the battery on this 7-8 years old Epirb would have been costly. I opted for looking out for a deal. It soon came along at Defender. I will probably keep the old unit and take it along on my little day-sailor. Then again, maybe, it will go on eBay.