Ok buckle up this is gonna be a long one:

I’d imagine robots in this universe have gotten to the point where they don’t need to be charged, more recently made robots like Noodle and Parry prolly do some dumb stuff like taking in oxygen or some kind of energy in the air to stay functional. Older robots though would need to be charged, they’d have to be OLD old, this technology has been a thing in this universe for quite some time now so these bots would be like elders at this point. There’s also the fact that robots like Parry can eat and drink, maybe some robots are able to convert that stuff into energy? I’d imagine it varies, like now some robots are waterproof and some aren’t bla bla bla it would vary depending on who made it and what they thought was most necessary for them. There’s my rambling of an answer