I've purchased several Mugen batteries in the past. I purchase one for my N95-1 and another for my N810. Both were the double-wides requiring replacement backs. Both batteries definitely provided MUCH more battery life, but I wasn't pleased with the quality of the backs. In particular, the plastic retention clips seem of poor manufacture and have broken on each. I've had to resort to painter's tape on the N95 back to hold it on and actually epoxied the N810's in place.

I would really like to get an extra big battery for my N900, as the battery life leaves much to be desired. I hope someone comes with a replacement back with charging contacts and an accompanying cradle, as I am very wary of the poor mechanical design of the micro-usb port. Maybe they could fix some of the camera issues while they are at it? Someone could make a lot of money selling replacement backs to fix Nokia's design faults.