Looks like someone tried to solder the negative terminal onto the battery.

Just use a big sheet metal screw and hope you never have to touch it till it's time to replace.

I wouldn't to near a battery with a torch. It's likely to blow up. Batteries can vent off explosive gasses. Sometimes just a spark near them is enough to make them explode. That's why you should always wear eye protection when removing or installing batteries.

I allowed the sparks from the grinder to get too close to the vent tube on mine. Sounded like a 22 shot. About three hours of baking soda and water trying to get every crook and nanny.   Went with the glass mat ,Big Crank to replace it.

The, coff, coff, welding rig at a place I worked had no tie down on the battery. I got some of a seat belt,  bolted it in good and tight. Coupla weeks later, sitting in the West Texas sun, it detonated. I'm guessing I distorted the thing and then when it got good and hot a coupla plates touched... My boss got lightly sprayed with a few drops of the acid, but not on skin and not enough to even notice, until the clothes got washed. Holes here and there..  The new battery was more gently secured.
I'm glad I quit tightening when I did. Woulda Sukkt being leaned over that thing when it desploded... There were chunks of battery scattered around.

A cigarette, boom... Hydrogen is not something to, pardon me, but I Have to say it, take Lightly.


More than I had a clue about....Wow,,

http://www.tms.org/pubs/journals/jom/0101/nelson-0101.html

I wouldn't be running a screw into something like that. Get down in there a ways and that thing stops but there's a plate of the opposite charge right there? Daaang,,
Phantom of the Opera,, but, hey, that's okay, cuz you'll probably be blind and will never see it.

Batteries are feminine.
Unpredictable, volatile, and can seriously let you down.