What you're calling the ESC is the 4-in-1. It has built in ESC's, a gyro and a receiver all built into one unit - just for clarification. You do not want to put two batteries together because that would up the weight. They wouldn't fit in the battery tray either. Use one until the heli is looking tired. Land it and let it cool for a while. Thn put in the second battery and have at it again. FWIW, the heat sinks/ cooling fins don't do anything spectacular to cool the motors. What DID make a big difference in cooling were the Aero-Nutz motors. They have big colling vents in the motor can, but for some asinine reason, the makers aren't cooperating with dealers and we can't seem to get them anymore
. Thus, the talk of going brushless.