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
LP-E6 Aftermarket Batteries » CheesyCam
One problem I've experienced with these... since there's no indicator you never know when your cam will quit on you. Usually it's not a problem. HOWEVER - i was apparently eeking out the last drop of power on one of these and the cam quit while playing back a movie. NOT A GOOD THING.
The 5d does NOT like this:
This resulted in the entire card becoming corrupted. Oddest thing ever - but they all showed up as jpgs and raw files - not movie files. Thankfully I was able to use 3rd party recovery software to get most of the clips back - about 3 were totally unrecoverable.
Just an fyi if it helps anyone... I now have all canon batteries, haha. I saved these for when i'm really in a pinch and now know not to go too long with them.
I use the after market grip as well - only had one problem once where it all of a sudden stopped me from adjusting aperture in the normal way. I took off the grip out of desperation to figure out why - and that turned out to solve it. Put the grip back on and it was fine. It might have just came loose - not sure.
72MM HD UV PL FLD FILTER KIT FOR CANON 5D 20D 28-135 :Dublinsnapshots