Lead-acid batteries are killed by being completely discharged. This isn't always true, but it's mostly true. They're happiest when they are left on a trickle charger which keeps them topped off and never discharged too far.
So, if you want a lead acid battery to last, you should either leave it on a charger where it can get a constant trickle, or, at least, take it out periodically and charge it back up. I don't know what frequency you should do this at.