you should definitely replace the battery also, especially since you've already gone through an alternator. The alternator when its flaky charges the battery at inconsistant levels, which really puts stress on the battery and significantly shortens its life-span.
To charge a battery at 14V isnt neccissarily bad, it just shortens the life [specifically because it essencially overcharges it, forcing it to hold more charge than is optimal]. This affects it in several ways, over time it will only be able to hold a fraction of the overall amp-hours of a new battery but it can also sevearly limit the amount of amps the battery can output. so with your supercharger, you are putting alot of additional strain on the electrical systems to quickly rampup/rampdown the amount of amps it needs to deliver and I just dont think your battery can handle it anymore.
just my 2 cents.... we did alot of battery work with my solar boat, and I can say our batteries never lasted long befor they were trash. I suggest getting a high amp output battery [either an optima red top or if you can find them the NASCAR Selects].