Review (4/5): Great product! But leave the battery cap off between uses...
Sonicare are great products, as my dentist has noticed.
The only problem with this great replaceable battery version is that the batteries didn't last for more than a week or two. Until I discovered that removing the battery cap between uses made the batteries last 2-3x as long.
I can only guess that there is a small constant current drain on the batteries. Removing the cap disconnects them and stops that constant 24-hour-a-day drain. Then they last fine. I use NiMH rechargeables.