When the battery goes below 11 volts its always best to charge it with the highest amerage available to help with sulfation, the extra temperature the charge creates will help dissolve the crystals.
If all you got is a 2 amp charge, its better than nothing obviously, but like i said i took mine to the auto parts store, where it went from 10.5v to full in about 2 hours+, it must have been a very rapid charger, which i am sure helped with the sulfation. My charger only goes up to 15 amps but i wanted a higher amp charge since it went flat.