Most likely dead, look at the plates, do they look bent twisted or broken ?
You can put in new acid to 1.280PH, but won't cure a dead battery.
A conditioner charger can often revive very sucessfully some dead batteries, the se conditioner chargers work in a different way to a steady state charger and are much better, last one I bought from LIDL for £15, only 3-4 amps but charge so quick due to the way they work, can can be left on 24/7 all year round, as it exercises the battery.
Sometimes they can be revived a bit by washing out, but hardly ever works.
If as it sounds the car is left long periods get a AGM, even fully flattened won't harm, won't cause sulphation like a std lead acid one, or other wise VARTA BLUE is the way to go.
tabetha