I use the LanParte shoulder pad with cheap CCTV batteries and a cable tie. Works brilliantly. 5V (sound recorder/HDMI sender), 9V (GH2) and 14V (LCD Monitor).
Lanparte battery pinch, as they call it, is quite standard and works only with Canon cameras.
As far as I know none of the firms make similar GH2 ready solution.
You can check other topics in http://www.personal-view.com/talks/categories/power-camera-rig for various options.
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