ELI5 AA Batteries - how did AA type batteries become standard and what about the A battery?

What makes AA batteries the go-to choice for so many devices when alternatives exist? Why do we have so many different battery sizes like AA, AAA, C, and D? What led to the standardization of battery sizes in the 1920s? Why do some devices require two AA batteries instead of just one? What factors contribute to the performance difference between name-brand and generic batteries? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: tmahfan117, twotall88, brianbell_, ccsica, jwink3101, reddit1651, wrsaunders, santhonyh To the community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [e-mail]