After Market Batteries
 

Quote from Accessory guide included with GZ-HD7 :
"JVC Everio includes patented and other proprietary technology and will operate only with JVC DATA BATTERY. ... Any damage caused by using other than a JVC Data Battery is not covered by the JVC Warrenty"

An additional after market battery was included with the HD-7 I recently purchased. The Sakar website specifically states this particular battery meets or exceeds JVC's specifications, although there is no mention of the "data" part. I've asked Sakar via email what their battery will or will not do when attached to the camera. No reply as of yet.

So, can anyone tell me what is unique about JVC's data battery?

Aftermarket batts
 

Waldemar:

We have a few of those Sakar aftermarket batteries.. The only thing I can see is that the camera can't estimate when the battery will die. You also have to use the little dongle cable (plugs in to the after market battery, and goes into the charging port on the camera). The camera has a rough idea, but can't give you that neat little information display it does with a real JVC battery.

Other than that - it does what it does - power the camera.

if you check power you'll see the hd7 gives a really cute graphics display. I bought the medium jvc at CC and am very happy with it. the tiny battery is useless.

So that is what that silly looking dongle thing is for. The instructions that came with the battery made no mention ... in text or in pictures.
Well, I tried it, and discovered the metal contact plates in the battery make contact with the camera's contacts, which brings everything to a halt. That might cause an issue with the battery in proper place and the camera turned off... would the battery not try to charge itself? Would that cause problems for the camera's firmware? No clear answer without JVC's opinion, and they are not talking. To be safe, I filled the battery's contact plates with silicone to prevent any metal to metal contact.
Fortunately, I didn't pay for this after market battery. It came with the camera ... don't know why. In any case, I buying a real JVC battery ... a big one.

The medium battery came with the camera. Only lasts an hour or so. Not enough. Going to purchase the biggest battery I can find.