Hi.. The Optimas come in 3 varieties...red is starting batteries, the blue is the deep discharge (house batt) Can't remember what the yellow is...maybe a combination?? Do a Google search on Optima and you'll find their website and more info then you want to know about batteries. Oh yes...you _DO_ have a good idea of what your current drain is, (hopefully) ?? I've only used West Marines little gel cell, and charge it after everyuse. Harvey/Ga M-17 Stargazer #294