The replacement Reatta has died now several times and I can't understand why.

I did find the positive cable loose at the battery but would a loose cable cause a running car to die?

Also there was a loud squeek. I thought it was the belt so I sprayed on the only evaporative stuff I had and that was some electrical contact cleaner. The squeek stopped. Great! Then all of a sudden the belt flew off. Anyone have a clue why that would happen? A new belt and no squeek. Old belt as well as the new one stayed on without the cleaner sprayed on.

Does anyone have a clue why the belt would fly off like that? This was a new one to me.

I would think the belt tensener throwing the beit. This car is very sencitive of the 12 volt system ,poor grounds,or drop in voltage,bad altenator will cause car to shut down.

Check all the pulleys driven by the belt. Especially the alternator. A bad pulley will cause belt glazing. Your spray test confirmed the belt was glazed. Look at the belt. Did it show excessive wear on the smooth or ribbed side?

A bad water pump bearing will allow its pully to tilt and cause a good belt to walk off the pulley