A ham radio club near me recently found a large, institutional UPS user getting ready to replace their big AGM batteries. This is done on a schedule, even if there's no reason to believe they're bad. They were five years old with a 10-year warranty.
The good news is, they got them donated free. The bad news is, they weighed 750 pounds each, and required a 3/4-ton pickup and a rented engine hoist to move. In any event, the repeater site's mains-charged emergency back-up battery bank is now set for another five years.
If you know people in the IT department at your school, see if any of those guys have contacts who might know of such opportunities. My wife would kill me if I brought a gigantic AGM battery into the garage, but hey - at least it would be hard to kill it with small charging goofs. Besides...I've been looking for a reason to introduce myself to that new neighbor with a forklift!