There are many chargers out there that will charge both 6v & 12v batteries. I prefer to use smart chargers to prevent overcharging. Schumacher brand chargers have been pretty reliable for me. Make sure you only charge your battery at an amperage rate no more than a maximum of 1/3 of the battery's amp hour ( AH) capacity (preferably no more than 1/4 of the capacity). I.E. if you have a 12v 12 AH battery, then you want to charge it at a rate no more than 3-4 amps.
2amps would be fine also. If you charge a battery at too high of an amperage rate then you risk overheating or "cooking" the battery. This decreases battery life. It's normal for a battery to become lightly warm during a charge cycle. A hot or "squealing/whistling" battery during charge is a bad sign. Hope this helps.