Flatbat - did you change resistance when you changed the coil? Lower resistance will draw more current at the same level of watts, but that sounds like a drastic reduction in battery life.
If you were at 2.3 ohms, 4.0 volts to reach 7 watts, the current is 1.74
If you went down to 1.7 ohms in your coil, then dialed in the same 7 watts at 3.5 volts, the current is 2.03
If you went down to 1.7 ohms in your coil and left the twist at 4 volts (9.4 watts) the current would be 2.35.
(Higher, but not a significant increase in current).
Like I said, I'm not sure if you would further decrease the life of your
batteries with a slower charge by sharing a multi-port hub. There is a 10-port 510 charger available, and it will also charge eGo batteries (but a 510-eGo adapter would be needed for each eGo). You'd want to confirm that the 10-port hub is compatible with a car charger for those long road trips.