So, my oral health therapist had a prolux that went defective after a year when attached directly to that mini battery. It just turned off and on when she turned her head too fast. I haven't had any trouble with my prolux which is attached to a wire. I've had mine for a few years now. I think the battery might put too much stress on the connection. It wasn't bad enough that I didn't just buy her another one. It's also possible that being a new user she just broke it. So some good but some concerns with reliability of the battery attached directly to the light.