Review (5/5): Works great, I'd rather have this than the expensive ones
My pet peeve in electronics is non-replaceable or proprietary batteries, so I always choose the standard AA model if it's available. After a little research, I found this performs exactly the same as the high-priced units and at a fraction of the cost! I already have tons of rechargeable batteries that I use in remotes, mice, cameras, etc, so I didn't even have to buy extras.
I can see how the battery compartment may not be entirely water-tight, but it's on the bottom of the device, so I think the problem may be that people are standing the brush upright when not in use. It actually has a little stand on the back of it indicating it's clearly meant to be laid down horizontally. If you stood it upright and did not dry it off, I can see how water could seep down into the battery compartment, but it's clearly not meant to be stored that way. Or as is indicated in another review, put some vaseline on the gasket to seal it if you're really worried.