Follow-up:
I received my carrot yesterday and decided to take it for a drive out of the box. I, too, had an issue with the battery. After about an hour and a half it began toning low battery. I did end up using it for over 2 hours, and it didn't completely die on me, but the battery it's packaged with just seems to be the issue. I'm going to buy a higher-quality and try again.
On the plus side, this thing is awesome. I'm still a newb at detecting, but I'm glad I invested in one at the beginning. Won't leave home without it now.