Boiled Optima = Alternator belt squealing? Options

[fiid]

I think I overcharged my Optima red top. It does hold some charge, but the voltage seems low, but still sufficient to start the car.

Problem is that my alternator belt now squeals like a pig for about 20 seconds or so after the car starts. You can even watch it on the voltmeter (a new VDO unit). Basically - system voltage sits around 12v, with the alternator squealing, and as the belt gets more traction - it rises to a healthy 13.8v - and the squealing dies off.

I was wondering if the battery is drawing enough amps before the voltage gets up that the alternator is requiring a lot of torque, and causing the belt to slip, and then once the voltage gets up and the battery is over it's initial hump everything works fine??

My belt tensioner is at the limit of it's adjustment, so I can't tighten it anymore, and it's hard to buy a belt that is like 1" shorter since there are very few catalogues that are indexed by length and rib size/count (it's a 5v poly-v belt). I'm thinking replacing the battery is a good idea, but I wanted to consult here and see if anyone has any better ideas.....

Thanks in advance....