I saw a post on a thread similar to this where a
ham said he purchased used
tank batteries from
the Army or the National Guard.
Sorry I can't give you more info re voltage,
capacity, etc. The fellow DID say that they
were big, heavy, and that he was quite pleased with
them.
Check with the local hospitals and EMTs. It used to be that they were required to replace all their batteries every 90 days regardless of their condition. That may still be true.
I asked the engineering staff about this at one of the hospitals where
I did my X-Ray Tech externship work. They said they would love to help me
out, but their policy was that since it was a "Hazardous Recyclable" item,
they could only let them go to a licensed recycling company.
YMMV depending on location and the hospital. Both Federal and, especially
here in CA, state hazardous recyling laws
are very strict.
GL ES 73, Ken AD6KA