I bought a CTEK battery charger. I really like it. It will work as a maintainer or charger. You can leave it attached and it will only charge as needed, shutting off when a full charge is reached.
The main reason I bought it vs a Battery Tender is that the CTEK has specific settings for they type of battery. It has a motorcycle setting that is really low amps (.8 amps) so it won't fry a small scooter or motorcycle battery. It has a regular setting for car batteries like in our GT500. It also has a setting for gel type batteries (Optima, etc) With the gel batteries it has the same amps as the regular car battery setting, but charges at a higher voltage. I've got an Optima in my race car, the regular battery in my GT500, and a Yamaha scooter I use as a pit bike with the race car. I can use the CTEK on all three.
These chargers also are oem acc for Porsche. Mercedes, Bentley and Aston Martin.
CTEK site:
http://www.ctek.com/EN-US
You can get them from many dealers, but I bought mine here:
http://cgi.ebay.com/ebaymotors/CTEK...62QQcategoryZ43989QQihZ004QQitemZ140250561060