Marine parts, but why not...   
2 Optima Deep Cycle marine batteries, work fine in a car.  Have had one in mine for 6mos.  As for all of the "If it goes dead once it is garbage" claims, you cannot use a basic garage charger, need to throw 50 or so amps at it.  (That is what they told me this morning) 
They were in a boat for 10mos, and in use on the water for a few weekends over 3 mos last summer. 
$75 each   
Also have a Dana Marine red billet battery box, looks nice. 
Retail is around 160, also asking 75. 
  http://img.photobucket.com/albums/v177/Hyperbaja/P1010293.jpg   
  http://img.photobucket.com/albums/v177/Hyperbaja/P1010294.jpg   
  http://img.photobucket.com/albums/v177/Hyperbaja/P1010295.jpg