These 5v 2000mah USB supplies and little USB chargers work well.
The multiport 5 and 10 port for the little 510
batteries would probably cook itself if loaded with a bunch of eGos.
I opened up 2 of the holes in a 5 port and that seems to be OK but I would not want to try more than that at once.
It didn't work that well charging 5 510 bats.
Rotating bats is a good idea. Reduces the load on any one of them. Not necessarily because you go through that many bats in a day, just distributes the wear and tear.