Would it be possible to configure it so that after a very, very long time they need to refuel at the roboports instead of recharging?

I don't know how the refueling would work. I'm not an experienced modder so I don't know how I would go about making the robots automatically refuel. Great suggestions though.

Or, instead refueling, dollect another cell and drop used ones in a logistic chest that contain some. Same as fuel, but for each robot. :P
I know, a but too difficult to implement, but for have a more realistic infinite energy bot I like better the fusion bots instead. Fusion reactor work indefinitely, so that the bot wont deplete energy is more ralistic than uranium cells that will deplete soon or later...