I thought this was old news and everyone was already using these. I purchased these batteries just weeks after the Canon 5D Mark II was announced! Yeah they are pretty old, but still rocking and rollin'. Apparently after posting my aftermarket battery video for the 550D & T2i, I received many questions on the 5DM2 / 7D aftermarket batteries.
So these batteries work differently. They don't charge on OEM canon chargers, and they don't display battery life. Other than that they are dirt cheap and work just as long (i think so). I'm also using aftermarket China 'battery grips' on both my 5D Mark II & 7D. Prices have gone up a bit. I purchased mine for about $10.00 dollars. The Canon 5D Mark II and 7D use the same type of batteries. I purchased mine from this seller. It's going for about $14.00 dollars. Click this link to purchase.
Battery Grips for Canon Cameras can be found here:
Canon Aftermarket Battery Grips