I had an original sealed battery - I think it was a Hella one, You can try to charge it, though mine went at about 9-10 years. When they get in this state, usually it is a dead cell so wont hold a charge anyway.
Get a new one, Euro car parts are pretty reasonable. I upgraded to a larger diesel version - see if your battery try can cope with this there is a second mounting hole for a larger battery
Oh yes, find a local scrap merchant and take them your battery - you'll need some ID though and you'll get some ££ back !