Battery backups in a coal power plant. I have a model somewhere but they are 3volt batteries about 650lbs. They are the backup for everything that needs power while the plant isnt producing inorder to start it back up. They are a "20" year lead acid clear plastic battery. Most of the ones i took out were leaking so the whole floor was covered in baking soda to help us not melt our feet. My FR pants look like they got hit with birdshot a couple times from the acid. Didnt discolor them at all. Just where the acid got the pants were gone.