Review (1/5): Engineered to fail
This product is good while it lasts; it'll clean your teeth better than almost anything out there (unless you have tartar, then you'll need something with a bit more power) and stimulate your gums. However, having autopsied this model, I am convinced that it was engineered to fail under typical conditions after a time, perhaps to motivate the purchase of a more expensive model, which will itself become useless when the irreplaceable batteries go out.
The first one I bought lasted a year, and even that long only after I learned that you have to plug the two holes in the back of the battery compartment to prevent the corrosion from taking place. By the end, batteries were lasting one week tops, at 2x use per day. I also learned that you have to hit it against hard objects when it won't turn on and sometimes then it'll go. You also need to scrape off any rust from the battery contacts occasionally.
Knowing these quirks, I bought another one and immediately plugged up the holes in the back and put tape around the battery cap. However, it has now lasted only a month. There's no rust or corrosion to speak of, however, it just doesn't turn on anymore.
Today I autopsied the first sonicare to see why it had failed (the new one is still on warranty). In taking it apart, it's clear that most of your money goes into buying a tank-like shell around the $1 worth of electronics. This would be a good thing, if there were not two gaping holes in the battery cap that let water in anyway and the shoddy rubber seal. After taking it apart, it's clear why the corrosion so quickly leads the failure. They protect everything on the circuit-board from corrosion by putting glue over it, except the battery contacts, and the contacts and wires that lead to the solenoid coil (that makes the brush vibrate). The contacts that lead to the solenoid and the battery contacts are also strategically located next to each other on the circuit board, so they can corrode together quickly using any moisture from the adjacent battery-terminal holes, while the non-essentials like the timer are located on the other side of the board and completely sealed off from the ambient air by glue. This also explains why hitting it sometimes allows it to start; you're shaking some of the corrosion loose.
The switch is also of questionable design, being nothing more than a paper-thin piece of plastic with some kind ring on it that's slightly more conductive than the plastic.
If the replacement that I get out of the warranty fails, I think I'll try a cybersonic or an oral-b; hopefully their teams of engineers weren't paid to make something less reliable than a politician.
Why can't they make a sonic toothbrush with no batteries, that plugs into the wall, and lasts a lifetime? Or just quit making these to fail so readily?