A video system needs an uninterruptible power system. Considering that it has only a 12 Vdc input, it's begging to be powered by a 12 V battery.
Sure, I have it on a UPS. But that's just so kludgy (AC => DC => AC => DC).
The most important part of this project is to find the proper battery. Should it be a deep-cycle SLA, Li-ion, or Ni-metal hydride? Or, perhaps there's a better option.