A friend gave me a group 27 deep cycle battery. Took a charge just fine. I bought a battery box on Amazon for $18. I plan on installing sometime this week. I'll probably paint the box the same grey as the other interior panels and sister it up to the rear RH shock tower.
The battery has enough cranking amps (675) to replace the current 12 volt entirely (the Geo takes 390 cold crank amps, best as I can tell).
