Car and truck batteries don't last long if they are completely drained. Even new ones. They are not designed to be fully drained like a deep cycle battery. They are designed to get recharged as they are used with the alternator. I found that if you keep the battery charged and clean in will last more than 6 years in areas like Colorado but here in Arizona I get 4 years. Newer cars have so many accessories that trickle a battery down when the key is out. If you aren't driving the car for a few days at least start it up for the sake of the battery. Otherwise disconnect it if it will be sitting for a while. I know its a hassle to reset everything when you reconnect but the alternative is short battery life.