How long does it take for a utility bot to recharge itself?

I have a cleaner bot at 9.34% battery. It says I can either tune it up or let it recharge itself. I've left it there for a few in-game weeks and the battery % hasn't changed.

Is it possible for a bot to recharge itself? How long do I need to wait? Do I need to do something specific to allow it to recharge itself?