Walter i understand the battery life on them is 5years ? our clock-setter has told us this ,will have taken view from Unikon information .i dont have the book-let to hand(were having work done on the house) .our club has had them now for 5 years ,and were expecting the worse , all members (15 flying lofts) use the mains ,most members only switch them on , on a Saturday .occasionaly for training ,1 member i know leaves it in situe all year round .so i/we could be wrong ,but would like to be in a situation where we have the funds to cover any failings.