I had a Phillips Sonicare and it died on me in just under a year... looks like it wasn't water sealed and you know the rest.
Then switched to the Oral-B, pretty sure they're not Li-ion. They do take an awfully long time to charge, about 24 hours.
It's actually the Oral-B Triumph 6000 I have, all sorts of stuff on it that I never bother with.. bluetooth and a gimmicky smart guide thing... never been opened.
Other than the long charge time, it is very, very good.
http://www.amazon.co.uk/Oral-B-Bluetooth-Technology-Rechargeable-Toothbrush/dp/B00K2U61FG
After a 10 year sabbatical from the dentist (bad experience put me off), I returned this year and the hygienist commented that there was very little plaque considering they hadn't been seen to professionally in 10 years.
Between the Sonicare and the Triumph 6000, I had a Triumph 5000 (which I still own), but I find that the battery just doesn't keep it's charge much after 3 years of use.