It can be a sealed lead acid battery or Gell cell (instead of the liquid acid it's a more of a paste). I'm not sure what radio shack has. If you have a good sales person they can help you figure it out. If not... Here's a link to a place I find some cool stuff. Here is a picture of the type of battery I was talking about. (You can search around to get more ideas) They have been good to work with if you decided to go mail order, but a local person is usually better if you're not sure what to get.
http://www.allelectronics.com/cgi-bi...EAD_ACID_.html
My best guess at what you need:
1) Battery (2Amp Hour is lighter, but 7 or more Amp Hour will last a lot longer - kinda depends on your requirements for size and weight)
2) Power wires or cable from battery (probably use crimp connectors (Insulated connectors are best choice) that slide on the battery terminals) You may be able to get a cable that meets your requirements and has a connector that can plug into your display or you'll have to crimp or solder to it.
3) Inline fuse (crimp type or may be built into the cable if you find one)
4) An in line switch or just pull the cable off the battery when not using.
I hope I'm being clear enough, without boring you to death. Like I said, a good sales person at your local electronic shop can be of great assistance in either finding a proper cable or pointing you to the parts to make one. RadioShack probably has a good selection of cables or things you could cut one end off and attach something to finish the project (maybe even a used old piece a connector in the junk bin that they would give you???).
How'd I do??