+1 to Everything koder said.. in theory , follow step by step..
1 - research which battery seller has clean acid.. most keep it in a blue drum and that oily and dirty acid..find some one who is either making fresh acid, or has a clean drum
2 - donot wash or drain battery yourself.. its very corosive.. will damage your drain pipes.. if you have a main sewerage pipe outside your home or at end of home, only drain in that, otherwise just take it to battery filler and he will drain it for you.
3 - you can buy either the exide liter or larger water bottles to wash the battery... or just , boil, cool , filter lots of water at home.. use that for cleaning.. i wouldnt recommend any cleaning though..
instead, just put nitto tape on the battery top screws holes.. screw them tight... shake the battery using 2 people atleats, shake it hard and immediately drain it.. the acid now coming out would be darker blaccker.. cleaning out residual deposits.. if you do decide to wash, use method above, and keep holes open and let it dry in sun for many hours before refil.
4 - get it refilled.. and make sure he pours 1.25 or slightly less, 1.23, 1.22, gravity acid. not stronger
5 - if you can make sure your ups can provide charging for 2 continuous hours,(loadshedding times) then charge on your ups.. easier is to let the guiy charge it at higher volts just for an hour and do the rest at home.
for an easier diagnosis, Shake the battery yourself, very rapidly so all the acid is mixed inside...just drain the battery using any hydrometer and see if the color of the acid is clear, muddy or blackish.. if blackinsh, battery passed its life..
then suck out excess acid upto the lower level mark and little lower., so that the plates of each cell become visible.. let it stand for a few hours with open caps to let the top ends dry... if you can easily distinguish between black and white plates sandwiched , your cells may have life.. if all you see is black, then your batery is dead..