how long will it run on battery only?

It doesn't accept batteries, must be plugged in via AC wall adapter. A good unit though.

Does this frame run on battery's as well as a power outlet?

I don't think so, though I have never tried. There isn't an obvious battery port and it has only worked when I plugged it in. I really like the auto timer feature though, I have it at my desk at work and set it to only run the hours that I am at work.