Well I work at a local auto shop. Just recently the military base has asked us if they can dispose there batteries and tires with us. I told them sure so we have a bunch of plane batteries and tires now. These batteries they have brought us are huge though. They are AGM batteries that are 24V. I have put a multimeter to them and they are holding a steady charge of 23V. I would try to charge it but my charger is a 12V.
I am assuming I cannot run it as a secondary battery because it is 24V while the car is at 12V. Does that sound about right?

Info on the battery:
Aircraft Parts, Aviation Supplies, Pilot Supplies, and Avionics from Aircraft Supply And Repair Inc.

Well here are the pictures.