vr,
That battery will blow out 12V lights pretty quickly. Some bulbs can be overvoltaged up to about 20%, but 50%+ is too much. A 5 amp hour sealed lead acid batter is only about 10 bucks and a nice charger about 15. Or you can get the power pack that Pete got for about $20. It is 4.5 AH, comes in a little bag, and has convenient car lighter type plug.