Agreed, and how will anybody but you know that you hooked it up to a battery rather than solar panel, I don't see how that could affect the warranty unless you told them.

One cautionary note. 6 AA cells is 9V, 6 of the rechargable cells are only 7.2V. A 12V solar panel will quickly drop to around 9V while charging a 7.2V battery pack, since it's limited to around 500 mA of drive. However, a 12V external battery would not drop because it can drive several amps, possibly quickly draining the external battery. I doubt this will cause a problem, but it could. I don't know what kind of internal voltage regulation exists inside the camera, but it was designed for solar, so it would not have any special circuitry to conserve power from an external battery.

Who wants to be the guinny pig?