Stef,
What are you trying to do, charge a down battery or maintain a battery during the off season? Or are you after something to quickly charge and or start a vehicle with a dead battey? To maintain a battery during the off season, such as a boat battery, a float charger is all that is needed. Inexpensive chargers offering 2 or 6A charging @ either 6V or 12V can be had for $25 or less. A unit used to quickly charge a battery or jump start a vehicle starts to get a little more expensive. Check out Harbour Freight, Northern, Tractor Supply, etc for more info.
Hope this helps, Larry