While these guys are giving good advice, I like Deb Walker's advice better: "If your battery is original, and your car is a 2004 or 5, you need a new battery. They tend to die without warning".

I ended up having my company's Dodge Durango refuse to run one day, $85 tow bill and 1/2 hour at the shop ($50 more) and all it was, was a bad battery! (It would crank, but not start. Acted like it was out of gas). That taught me a lesson:
I changed my Roadster's OEM battery this fall before venturing out to the Dragon. $90 well spent at O'Reilly's.

Even if the battery IS NOT your problem, it is still going to BE a problem. Get rid of it.