I would look into a "Battery Tender" (that's the name) from Deltran.
www.batterytender.com
Its the only one I would use. If you look on their site there is a lot of info about how a battery is charged and what happens when it is hooked up to their charger. More info then I ever knew. A little more expensive but well worth it. I've had mine about 8 years and have charged dozens of batteries with no problems whatsoever. I am currently charging 6 - 6 volt batteries for my golf cart with it. Its the smartest way to go if you are going to keep batteries charged.