Can anyone link me to an automatic tending board for (2) 3.7v lithium cells in series? I want to run the Arduino 5v from the car source. I tried buck-down converter, but I think I'm having issues. It's probably safer to run clean power from separate battery.
Buy a Syma X8C quadcopter and have a look inside the 10V to twin-lithium-in-series recharge controller-balancer.
Why series when you can do achieve the same result with parallel? 