That was my other fear. But i think i will use both motors at the same time only on monster hills. The thing about electric, that I like and hate, is it only flows when you tell it to. I don't have to use both circuits at the same time. What happens when I do is anyone's guess. But I promise I will let you know sometime this week.
Frankly I'm not worried about some last year's batteries, I'm worried about the controllers and motors.