My truck has 2 batteries, and I usually replace them every 3 years. Usually a 400-500 bill, and about $50 per for a core charge.

I ran a battery charger out to it to keep them topped up. Even when I was driving it every day cold starts and weather beats the crap out of batteries. I've been on this set for almost 5 years now and they still load test okay. Ill probably replace them next year some time.