As far as a GPS up front, it is invaluable when trying to find or stay on a brushpile.

I'm not sure what you mean by 9 amp batteries. Do you mean 9 amp-hour batteries? A color unit will draw about 1.5A, so assume 4.5A for the 3 units, which means two 9AH batteries would only run the electronics for 4 hours at best.

Putting batteries in series adds the voltages, so if you want a series combination you'd use 6V batteries.