Is indeed a small world on the web.
Yes, Silver Calcium is required for the smart charge system fitted to your car. You may find your battery has had a few too many over voltage charges and its giving it grief.
The principle behind it is simply Ford believed that a battery can be recharged quicker and faster when cold. So the computer in your car takes a measurement of the engine temp, air intake temps and I believe the coolant temp. Working with all this, it decides whether to boost up the output voltage of the alternator. This means sometime the alternator can be hitting the battery with upwards of 15 or so volts. This has been known to cause issues with lead acid batteries, where they'll give up and die or most likely boil over.
The Silver Calcium batteries have a much higher tolerance to this higer voltage and take it far better. This may be why your standard battery is giving your electrickery such a run for its money.
Thats a damn decent price from Ford, so I would bite their hand off for it.
Regards the alternator belt, I would buy one once you've checked the condition of the old one. I had to replace one on my old MK TD lump, but that was because the power steering pump had been leaking and had deteriorated the condition of the driven surfaces. (fooked it!)
Best of luck with your new battery, failing that I guess its time to bite the bullet and hook up a new alternator. At least this way though you're going with the cheapest option first.
sorry about the delayed response (stupid BlackBerrys just arent compatible with this site)
now its finally all beginning to make sense!!! i cant thank you enough for helpin me diagnose this fault, for some reason i knew it was something simple! now lets just hope it lasts another week until payday so i can drive 70 miles a day to and from work (yeah im apprehensive too). the battery will be bought and i will report my progress here and on pistonheads. and i hope i dont have the same alt problem as you did but i reckon its not old enough to cause the squeeling that it has after being fitted in 2010 and only doing 20.000 miles, should i just buy a set of belts and have them done for piece of mind? for now its a battery though and need sort my squint steering wheel and the fact that its vibrating my whole body when i go over 60mph. balancing and alignment will cure this i think