Unless charging the camera every day, I wouldn't worry about the sealed battery. iphones have sealed batteries too, and those seem to last a few years even with daily recharging. I've owned the original Contour Roam for a few years and the battery still works fine (recharging about once a week). Battery lasts about 3 hours at the highest resolution setting, which is an hour more than other Contour cameras (presumably because the sealed battery is larger than the replaceable batteries used in the other cameras). The sealed battery also makes the camera more weather-resistant and the camera doesn't suffer from battery connection issues like some many sports cameras with non-sealed batteries.

The main problem with sealed batteries is that you're out-of-luck if you want to shoot more than 3 hours of video in one day. With a replaceable battery, you can just pop in a fresh battery (along with a fresh memory card) and keep going. On the other hand, the Contour Roam is really easy to turn on and off (unlike most sports cameras), so you don't need to shoot 3 hours of continuous video to get a few minutes of useful content. Just turn the camera on for the best parts of your bike ride.