Switronix has released a new power cable for the Panasonic GH2. The new power cable, affectionately known as the Switronix XP-DSLR-GH2, “can be used in association with a Switronix accessory or used solo with a PRO-X series lithium-ion battery product.”
For example, using the Switronix GH2 cable with the Powerbase-70 battery gives the GH2 over 8 hours run time. And, you need more, there are higher capacity batteries available.
More details on Switronix’s website.