I just got one of these batteries, and feel obligated to share my experiences. You do need to carve some plastic away from the terminals AND add some tape (3-5 layers of Scotch for me) on the back (side opposite the terminals) for it to work*, as has been reported. It feels a bit tighter getting it in vertically, but is horizontally shorter (hence the tape on the back). Haven't gotten around to testing yet, will report when I do.
*Works fine out of the box on my C750 (used to charge the first time as I was using the C3100 at the time).