I am sure of the exact battery life between charges, but it can go for a 
pretty good while, although it never hurts to have an extra battery pack. 
You might even find a longer life one at Batteries America or one of the 
other outlets.

As for the battery shell, It's probably not a bad thing to have, but those 
double A batteries, even the lithium ones don't have much transmit power. 
They are mostly good for monitoring, or at least that is my observation. 
73.
Harvey