I had been having battery issues with mine - until I started to remove the battery between imaging sessions. It is a little bit of a pain, but nothing compared to the battery running out halfway through the night. The cheapie ones don't have an on/off switch, nor do they turn off automatically after a period of time.
I have been thinking of strapping one or two AA's on the back and wiring them in with an on/off switch. Cheaper, longer lasting batteries, easy to change in the dark....cant go wrong!
