Recently have been doing a lot around batteries, as it seems to be the Achilles Heel of the 7D (and likely the T3i and T2i). When I bought my 7D early last year, I had the standard Canon battery with it, and also bought a Maxtek and Power2000. The Maxtek is now not holding a charge. The Power2000 still is holding up to the Canon battery.
I've also invested in aElipz along with the aCK-E6 power adapter for the 7D. This combination is fabulous. It has freed me up to shoot for hours without thinking about battery changes. It mounts to the bottom of the camera, and then mounts to the tripod. I have found that hand holding is not too bad, as it gives me a palm sized grip on the camera. I'm exploring mounting it on a shoulder mount though.
All in all, thumbs up on the Elipz and the 7D. Now just wish Canon could pull as much juice out of 7D battery as it does out of my xf305. I can shoot for at least two hours per battery charge, which has made carrying the elipz for that not worth the weight.