smoking battery...now dead?????

Just recently ( two weeks) when I start my 1998 2ltr petrol vw transporter in the morning, only the first start, the clock and electrics cut out for a second... then start working again! and the engine is runing with a little blip of a cut out every now and then!
now, just today, on a long drive, I could smell battery fumes in the cabin while driving, had a look and the battery is steaming!!! and is now dead!!!!!
The battery is a calcium/calcium sealed type, with no water top ups able!!!!
Could this be an overcharging alternator? or perhaps the coil is stuffed?