I dont know the only thing I can tell you i always did was carry a good spare one around in the glove box and in the tool box..if it started acting "bad" as you say the first thing I did was switch out the possibly "bad" one for a new one...easy to tell ...now if the one you switched was bad also your out of luck lol. But I always tested them on running cars to be sure they worked fine B4 putting them into "reserve" service.