@a2j 24 December 2021 more from that month

Why are 9 volt batteries shaped different from the others? While all others are usually cylindrical, this one alone is cuboid shaped and not circular. It also has its contact points on one side with the ability to clamp into the holders in the toys or instruments they are meant to fix onto. What do you use 9 volt batteries for? My guitar has one as part of its pick up.