Unfortunately, replacement options are limited. Definitely try putting it on a charger first, at 4 amps or less. If that fails to bring it back to 12.4V after sitting overnight, then the two popular replacement options are another one from the dealer or an Optima Yellowtop deep cycle. I did the Optima conversion using the elearnaid.com kit and am very happy with it. Lots of stories and opinions here if you search.
You want a AGM battery with a vent, as the battery is in the passenger compartment with you. You do not want battery acid or fumes/gases loose around you or your loved ones. The fitment is odd because of the JIS battery posts, but the elearnaid kit handles that. http://www.elearnaid.com/12vo1topraub.html