I think it depends on how far gone it is ... you could test it with a hydrometer, or take it to a local car accessory shop, who might be able to give it a good recharge for about a fiver if it�s in a reasonable state.
If it`s a low maintenance type (ie you can`t top up the water/acid) & it`s not so old to have just expired of old age, then give it a 2/3 day trickle recharge (the meter will show a high rate of charge initially but then should settle down to about 1 amp). Has it been sitting around doing nothing for a long time, or flattened by starting problems. Oh, & how old is it?