One should never leave a battery in storage without a trickle charge. It not only loses its charge but also calcifies the battery even to point of destroying the battery. I leave mine in the garage that never goes below freezing and has a small solar charger on it at all times. It will last a lot longer that way.
12 years and I have yet to leave a trickle charger on my batteries, they go through freezing temps often come winter, and I've never had a battery go bad. 8 years on my Starcraft's 2 12v Interstates, and so far 4 years on the 6's. There are many roads one can take to long battery life.