My main bass has a 9V for the pre and a 3V for the LED's in the fingerboard. The latter is replaced when dead - that happens about every 18 months. First the blue LED goes but i can go on with the red for a few weeks, then it's dead. The 9V lasts more than a year, but i happen to replace it before a gig when it's about a year old, so there are no nasty surprises on stage.