1st off, I have no business doing anything with a stick welder

I'm just doing this as an experiment, and the battery is not in the car.
My typical charging deal is limited to a 2A maintainer, though that's not enough for this battery - it needs the 10A setting on an actual charger.
The charger's 2A setting only results in a "bad battery" light coming on, and no improvement in V reading.
Checking battery voltage, it never shows better than 13.6V (charging), drops to 12.6V when charger's disconnected, then decreases from there, but never worse than 11.5 now.
It'll sit at 11.5 for 10 hours or so now, whether the desulfator is connected or not.

Interestingly, this resto battery never vents vapor through its caps; my other one does when on the maintainer.
The other one also had insufficient level inside it when I got the car.
It "runs" 12.6V (charged) down to 12.0V if left to sit a couple weeks, Ground cable disconnected.