Battery life on the pack that the GXT1000 comes with sucks. It's a 700 mah pack. I have probably 8 or 10 of the GXT1000s and on each one I just use rechargeable AAs and get days of use out of them. They're around 2100mah I believe. The OEM pack would be dead after a day of moderate use, and I loaned a GXT1000 with AAs to a buddy of mine for our sole means of comms in Moab for 3 days and it still had juice when he gave it back to me at the end of the trip. I have an 8 AA battery charger that plugs into a USB port that I use, charges them back up overnight just fine, but I also always have a spare set of 8 batteries ready to go.
Trying to tx from inside a vehicle is going to limit your range quite a bit too. With mediocre to perfect LOS (line of sight) I've been anywhere from 20-30 miles with my GXT1000s. On trails, in canyons and such, it drops quite a bit, but always works enough for me on the trail. I have MXT275s mounted in both our Jeeps, and then I'll grab a GXT1000 when I get out to spot too.