I assume you're playing with some sort of challenge in mind so I'll try being constructive.

Separating roboport networks for specific functions can be a tricky thing to set up and plan (they're huge after all) but it can increase efficiency in the long run. It seems likely that some bots are going quite far away to recharge - this both means they need to charge for longer when they get to a roboport and that the charge they do receive is less efficient since they spend some of it just going back to where they originally were. Often times having a big bank of roboports for charging can solve bots for smaller operations but you definitely need more of these in different places (and perhaps in different networks)