B&H is selling them for $25. Sheesh, I paid like $75 for one of them...
Power-2000 DMW-BLC12 BATTERY PACK f/PANA DMC-GH2 ACD-336 B&H

darn, I was really hoping to have to cobble a DC coupler together out of wood.

Sheesh, I paid $70 after shipping for an extra. At least it's a Panasonic branded one. Still, though, Panasonic really dropped the ball on this system. Cameras sold out, no batteries, small selection of native lenses. Sometimes I wonder why I adopted this system at all.

You cannot go wrong with a genuine Panasonic battery. I ordered two of the ones listed above, giving me a total of five batteries, but I kind of wish I hadn't, they are not fully decoded, or whatever they call it where it is not fully functional like a OEM battery. Also, using a generic battery may jeapordize your warranty, but I do not know that for a fact.

I bought another from H and B Digital for $65 delivered yesterday. The generics are cheaper, seen them as low as $15 delivered, and I have a stack of good working long lasting generics for other gear. But, seeing "The camera will not display power info while using this battery." caused me to go ahead and pay for the Panasonics.

While I could buy three or four generics for the price of one Panasonic and keep them fully charged, I'd have to guess when I'd need to replace the batteries so they don't shut the camera down during an important shoot. That's one more thing to have on my mind I'd prefer not to. Since I don' buy batteries every day and don't plan to have a case of them on hand, the difference in price is relatively small. It's worth it to me at this time. When they're fully decoded I'll happily get generics.

Adorama has Panasonic DMW-BLC12 Lithium-Ion Battery for Panasonic DMC-GH2 Camera back ordered but at least they are $59 with free shipping.