My wife works for a local charity and when they do fund raisers and such, they have an electronic picture frame that they use for a slideshow to show what goes on at the charity.
The frame came with the standard little powerblock that plugs into the wall, but they don't always have a convienant outlet and wanted a battery option. couldn't find anything available.
I went to Sears and got a 12volt Lithium Ion Battery and charger and came up with this. It runs the screen for about a hour.