Can work, but on a 6/7/9008 you are better off using a 8.4 volt pack to connect to the power-in. Makes the camera much more dynamic

Unfortunately the 9 volt connector has no securing. Also it could short the pack causing some serious fireworks and burning down your home or car. So you need a switch on the pack to switch it on only when the plug is in the camera fully. There are 3.5 jack plugs with a midsection non-conductive part. These should be fine here.
On 4008 you would need 0-3.6-7.2 volt. So you must modifiy the wiring of the pack and find a method to connect the pack to the metal clips in the batteryholder of the camera. Check the site of super8man
