You could try parralleing it up with another battery whilst on the charger but Id say the cell have gone below economical recovery
Your probably right, ive just been out now, i put it back on the optimate at 9 this morning, and its still charging -
So that's 11 hours and still not into the discharge / charge check - my money is on fubarred -
funny ive just seen your name on another forum, one and the same prehaps ?

