orrie smith wrote:
have you considered a battery grip for your camera. that way you could use both batteries in your camera and when one discharges, the other will kick in and you could charge the battery that is low on charge.
While not addressing the OP's original concern I want to state that this system wouldn't work with Canon battery grips. The camera doesn't use all of one battery and then switch to the other one - it depletes them roughly equally.
I have the original Canon grip for my 7D2 and actually run with four (4) batteries. I run them until they flash warning and then I swap both at the same time.