I've had batteries last anywhere from a year to over ten years. The one in my plow truck is going on 7 years, the wife's truck was just replaced and it was 10 years. My daily driver had new batteries 6 years after purchase from dealership. For living in -40 degrees and having hard winters, that's really good for the battery.
With the signs of corrosion, there's likely an issue inside and time to get it replaced. Either swing by Orielly, Autozone, Carquest or similar chain and have it swapped out.