Not a thing, those old ones were just dumb transformers with no controls to bring the amperage down. But you cant buy those new anymore. Its the same as new transformer welders, I wouldn't trust a cheap inverter like what's in the video unless you know it's a throw-away unit.
Run the welder in DC mode, Electrode positive, ramp up the amperage until it starts boiling (around 80-100 amps for car batteries) and let it chug away for 5 mins. Let it cool, run a battery load tester for 10-20 sec to discharge it and repeat the process until you either fry a cell or the battery load tester tests out good after a 10 sec draw. Do all of this outdoors when there is a breeze blowing away from buildings and animals. One battery had a hydrogen pop 3 times and that is currently my best one of the bunch, its rated at 600CCA and tests out to over 1100 amps.
Edit, again, these were completely dead, sitting in a snow plow truck bed for years through multiple freezes and thaws. If you have a battery that just slowly died in a daily driver you could probably bring it back around with only 1 session on the welder. Your just baking off the oxide layer (or whatever that hard layer is) on the lead to expose fresh lead. As long as the acid didn't leak out you just have to add water, water evaporates, acid doesn't.