I'd buy a low amperage smart "trickle charger" to maintain the charge. And when it is fully charged, check the voltage. I should be 12.8 v for a battery in excellent condition. It should be 12.6 volts or higher. If lower, it probably has suffered some degradation due to sulfation when it was deeply discharged. Some of the new smart chargers has a cycle that attempts to diminish that condition, although I'm not sure how successful they are. Lead acid batteries are damaged by full discharge, although the designated deep discharge batteries less so.
In checking the voltage, keep in mind that the charger can put a surface charge on the plates, much like a capacitor, and the true voltage will not show until the charger has been off for a while.