Originally Posted by SouthArk370Z

Depends on the state of charge now. If you have a few hours, I'd put it on 2A. If you are in a hurry, go with 6A. If the battery needs the extra amps, it'll take it; if it still has some charge, the charger/battery should self-regulate (if everything IRL worked like theory). But many chargers designed for charging a battery cannot properly float a battery.

The more I think about it, the more strongly I want to suggest buying a new float charger that is designed to maintain charge during storage. You can find cheap ones for $10 and better-than-adequate ones can be found for $30-50. As others have mentioned, over-charging the battery can kill it. It can generate enough heat to cause a fire (not that likely with a small charger like you have), and can even release enough hydrogen gas to be an explosion hazard (always possible, so make sure the area around the battery is well-ventilated when charging).