I agree with the Generator way to go.....

Tried carrying around deep-discharge batteries, but they didn't last long on the field, and are more heavy then a generator.

I bought one of these Kipor 1300 (the red one, not the sine-master), much lighter then the batteries, run's the whole day on 1.5 liter gas. And you can put up to 4 chargers up to it without any problem.

Yes it's more expensive at the beginning, but after the second or third battery ;-)

Have Fun
Winfried