I "hacked" the Sonic Trial brush. With a corded AC/DC adaptor that is. It involves using a Dremel (lucky you) or like me, a hacksaw and cutting all around (not through) the handle at the seam. The batteries are potted into 1/2 of the handle with epoxy, forget about replacing them. I cut the leads going to the batteries and drilled/filed a hole in both halves of the base to allow the adaptor cord to go thru and soldered the wires to the leads for power. Then, the momentary off/on switch makes you have to hold the switch all the time,... you can't do it! So... take off the silicone cover on the switch, and look and see where the traces are close and scrape off the green protectant down to the metal and solder the two traces with a bridge of solder or a strand of wire. Then, go and test fit it back together and try it. The off/on switch is now plug/unplug the adaptor in the wall. I then held the two sides together with tape and epoxied the two halves together, don't forget the threads and inside where the brush assembly goes to make it drool proof and rinse-able. Let's see... 2-3 hours work (much less with a dremel) for a $1.0o. But.. I have a working corded Sonic instead of a rechargeable one that was +/- 70 bucks new last time I looked. BTW, (as if anyone else would do this, I had a variable voltage adaptor and it runs best at 4.5v. You might substitute the adaptor with a RShack 2 battery holder attached to the cord and rechargeable batteries)