Review (5/5): This is the Sonicare model to buy.  Seriously.
This is fantastic. Free yourself from Philips' non-replaceable-battery tyranny! In their high end toothbrushes, Philips doesn't use Li-Ion or even NiMh rechargeable batteries. They use cheap Ni-Cd batteries that no one else has used for 20 years. You can't even buy Ni-Cd rechargeables if at your local retailer if you wanted to, because they are so lousy nobody wants them. And to top it off, they make the cheap Ni-Cd batteries non-user-replaceable.
This means when the NiCd batteries die (won't hold a charge), and they will, SOON, your Sonicare toothbrush is useless.
Unless you have this one.
It's just like the other Sonicare toothbrushes, except you can put your own rechargeables in it. I use Sanyo Eneloop. They run the toothbrush for about 6-8 weeks (compared to 2-3 weeks for a new Sonicare). Then you just pop them out, recharge them, and pop them back in. And the Eneloops, because they are a modern battery, will survive over 1500 recharges. And if the batteries DO die, replace them, and this toothbrush will go on forever.
I'd fallen victim to Philips' trap twice before, when I had to trash two Sonicare's due to failed NiCd batteries.
Now I am free from their battery tyranny. All their toothbrushes should be made with replaceable batteries this way, and the fact that they're not is just to force you to buy new ones (otherwise they would use modern battery technology.)
Don't worry about other reviews saying this toothbrush shorts out. It's perfectly sturdy and reliable. Just don't drop it in the water. It doesn't matter if the brush end gets wet, it's only the battery end that can't be submerged. Unless you plan to use this toothbrush while swimming, this is the one for you.
Best Sonicare toothbrush I've ever had, an the last one I will need to buy.