This is the perfect charger IMO.
http://store.schumachermart.com/sem-1562a.html
It charges Both 6 Volt and 12 Volt Batteries. and it does it at a rate of 1.5 Amps, so it will not warp the plates inside of the battery.
It also automatically switches to a float charge, so you can leave it on for a long while if you choose.
I have several of them I use for my motorcycles, and they have worked flawlessly.
-Best of all- Walmart sells them for $18