The back would make more sense. But his charger is portable and he just kind of stands in it in my room when he needs charging. It's not usually an issue like this. I'm not the one that originally made and designed him okay, that was Tadashi.

[Not to say that Hiro hasn't needed to deal with Baymax running on low battery before, but he was always able to get him home to the charger at least. That and....well, he wasn't going to comment or touch on the pervy comments there.]