I purchased a Dolgin DC to DC converter for my XL1, and now use it for the XL H1. It converts 12VDC to 7.2VDC. I bought some 12VDC bricks used for emergency lighting systems, and modified a CD player carrying case with a shoulder strap to carry the battery. The DC to DC converter came with a dummy battery shoe that fits all XL series cameras. I'm sure if Dolgin felt that there was a market for a DC to DC converter system for the HV20, they would start producing it. They are problem solvers, so it might be worth contacting them....

http://www.dolgin.net/