I have 14 of them (had 16 but gave one away and the other went with the Sierra when it was sold), they are UPS batteries from a data centre, story was they were ordered as replacements but they didn't meet some requirement and so were no good, and to dispose of them would've cost quite a lot (full of lead and acid) so they said "take some home" and I did...
I have two attached to an APC 1500va UPS, my entire computer room can run for around 9 hours without mains power
Also had one as the cranking battery in my old Suzuki Sierra, worked quite well though over time the heat and vibration slowly diminished its capacity.
I like to think that in the event of a zombie apocalypse I'll have a bit of extra juice when everything turns to shit, and when the batteries go flat I can use them as blunt weapons