If you have Optimas you want a charger that can charge 100amps for 15 minutes at a time, Black and Decker makes a model called the Vector that is very good, Shumacher Makes Nice stuff also. Get the best one you can so you don't have to buy another too soon.
I've got a Xantrex in the Cig. It's been flawless for a couple years now. Works great and simple to install operate. I've got Optimas and it charges them fine. You can program it for the type and size batteries you have, so it cycles and charges accordingly. http://www.xantrex.com/web/id/180/p/1/pt/7/product.asp