Cosmo It may have been the alternator that took out your alternator. Let me explain. If your alt was going bad then the battery may have been a victom of the Alt. Once the battery went it may have expedited the demise of that alt by over working it to death.

Here is an example that I used when I sold auto parts.

Your battery is like a large glass of water. When you start your car/ truck the starter takes a good size gulp out of the battery. The alt is like a pitcher to refill that glass. However the pitcher ( Alt) only has a small spout so it fills the glass slowly (over time). If you try to charge a dead battery with an Alt it is like trying to fill an Olypic size pool with a hose the size of a straw. Not going to work real well.
The Alt job is to top off the glass and run the accessories. In other words it is made for light( ( or lite work) duty. Battery Chargers are made for Heavy duty work.

By the way 4 years is good for a Battery.

Brian Moore
1949 3100 5 window Deluxe
"Today is better than yesterday, but not as good as tomorrow"