Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
The belt is self tensioning, (as you know) and there aren't any specs on it and they do seem to "bounce" a lot when the engine is running. The serpentine belt would make a alot of noise before it would slip enough to cause a charging problem.
From what it sounds like, the ignition timing could just be off some. I normally will unplug the wire at the distributor and see how it cranks. There is what is called a starter draw test, which will be very high when it is draging when starting, (like a ru-ru...ru....rarum) LOL, it's hard to translate.
However, if the battery cables have too high a resistence it will do the same thing, like a bad starter. If you can, you may want to do a voltage drop test on them. HERE is a link to a video that covers voltage drop testing.