When I do use mine, I maximize battery life by running batgraph and leaving it docked with the driver running on my PC. As long as the battery indicator is showing a lightning bolt, it's being powered via USB. I've left it that way for several weeks without it draining the battery. It must be powered on and batgraph seems to keep it from going to sleep while it's running and docked.
At least, that's how I remember it working, it's been a year since I last powered it up.