Good battery recommendations above.
Regarding charging, 95% of the time, I charge my batteries using the scanner through the USB cable either plugged into the computer, the car (it has a computer with a USB hub), a cigarette plug transformer, or an AC transformer (iPhone, etc.). 95% of this charging is done while the scanner is running. Some might attack this practice, but it is incredibly convenient and works well for me. Of course, if you want maximum longevity for your batteries, let them do complete decharge/charge cycles, don't let them sit low or empty for long, and use a good external charger.