What it the battery's voltage? Is there a way to hook an external battery to it to allow longer run-time?
I'd like to use it in a motorhome and have the 12 volt batteries as the back-up power source. That would allow me to run the motorhome off AC when parked and off the UPS when driving.
Mine is running at 120 volts right now. I would not try and connect a 12 volt battery to this, but you could daisy chain more than one UPS in order to have multiple layers of backup. Of course, the goal is to have the UPS keep things running until a generator can kick in, so that is really the better solution.