I have tried the 9v DVD batteries, but not extensively. I have since found these batteries:
http://www.neximaging.com/product.asp?id=42684&ADTR=9I think these are branded as "PowerPal," "Powerbank" or other names. They have a selectable switch to output 5, 6 or 8.4v, so I have been using these when I need more juice. I would think that the 9v batteries would be fine, but I was pretty paranoid about plugging it in like that. Plus, I found a good deal on the Powerbanks.
The times I've run the videocam, the setup I have is third party high capacity battery for the camcorder, and a couple of the Powerbanks. Having the camcorder battery allows me to swap the battery packs.
I've found that the Powerbank can go for 1.5 h and drop to 3/4 capacity, according to the meter. So between the Powerbank and the camcorder battery, I've never had a problem.
I bought the third party battery off eBay, and it was pretty cheap $20 if I remember correctly. The drawbacks is that you can't charge it when attached to the camera, and there is no indicator to how much juice is left.