Well sure the battery can be replaced, but we’re trying to limit what we throw away and avoid polluting the environment - especially when such pollution serves no purpose. Batteries require lithium and that’s getting harder to come by. I read some very disturbing news about prospective open-cast mines in Spain that could ruin the countryside and local ecology. The best solution is recycling, but that’s too expensive at the moment. Are the batteries are too cheap?
But to get back to the hub thing : did you read this post that Incanus pointed us to? It turns out that although using a powered hub didn’t allow the FP to charge, it did slow down the discharge rate substantially. The best result was with the following combination:
Fairphone 3 + ICZI + DisplayLink + TV USB (providing the power, as the ICZI isn’t itself powered) or a 45W charger ; the discharge from 85% to 80% took 32’ as against about 29’ for the FP alone with nothing connected. So that’s 10% per hour.
So this would also have the advantage of not flogging the battery (if I’ve understood things aright) 
Why not ask @serl 's advice?