The battery in this product is excellent - I bought it to replace my original (dying) offical HTC battery. Originally, I could make about 36 hours with the HTC battery (recently reduced to about 1 hour), and that is under "light use". With this battery, I can easily make it through 2 and a bit days without running out of battery, and that under "normal use" - update sync every 3 hours, some gaming, some videos, music, plent yof web browsing and IM, and a few pictures here and there. So the battery is a 5* product (I don't care that it's big, I knew that it would be, it's a trade off)
The replacement back cover is of lower quality - the fit isn't quite visually perfect and it looks "not the right size" in places. Seems to be well sealed against dust despite this, except for the camera hole which, oddly, doesn't have any kind of plastic covering - so the real camera is exposed to the world. Despite this, the material is pleasant to touch and sturdy, and there's an unmentioned benefit of the bulkiness - the phone can now stand (solidly) on its side for watching videos/displaying an alarm clock/etc.