CTEK Battery Chargers/Tenders at Maximal

[Maximal]

If you store your car for the winter you need one of these. Been using something similar to these for a few years but am picking up a CTEK this year due to the extra features. They're all cheaper than a new battery...

All are designed to use with 6v, 12v, and your AGM batteries (Optima, Odyssey, etc) and use smart charging technology to make sure you don't overcharge your battery. These things are pretty amazing as for example, the 7002 does the same thing as other cart-mounted chargers do, but in a case the size of a small shoe.

The CTEK .8 is great for maintaining your already charged battery. It's also designed to charge lawn mower/ATV/motorcycle batteries but will charge a car battery as long as you're patient.
CTEK 0.8 Battery Charger - Maximal Performance - Mitsubishi Performance Parts

Take a step up and get the 4.3 that allows you to not only maintain but charge automotive batteries. Great all around charger and the most popular of the ones listed. Has 4 stages of charging too.
CTEK 4.3 Battery Charger - Maximal Performance - Mitsubishi Performance Parts

The 7002 gives you all the features of the 4.3 but also allows you to "recondition" batteries that can bring a completely dead battery back to life most of the time. It also gives you a few more status LED's so you can see what level the battery is charged to.
CTEK Multi 7002 Battery Charger - Maximal Performance - Mitsubishi Performance Parts

If you have any questions let me know!