Last month I purchased an extended life battery.
When the battery/cover arrived, I went to intall it, and noticed that one of the alignment pins was improperly aligned.
I contacted the retailer, and they were going to send me a new cover.
I made sure to make the issue that the alignment pin on the upper left corner of the cover (looking at the back of the phone) is aligned properly.
I'm posting this, so that for anyone who does decide to get an extended life battery--- look closely, and pay attention to your phone's back-- alignment pins, and the cover-- look at the photos, and ask for photos of the cover-- specifically the pins.
I wound up having to break an alignment pin off just to get the cover to work.
PAY ATTENTION to what you're buying.