in my experience the positive plate expands and corrodes and litterally crumbles apart, well before the battery should have reached end of life.
This is always why I took these " Restore a dead battery " products/ devices/ gimmicks as hogwash. You can't just add powder or a devise to a battery to restore physical Damage...... Or so I thought.
The other things is the lead that comes off eventually piles up on the bottom of the cells and the thing self shorts.
I guess it depends on the individual case but I have to wonder how much of the lead can be Re-deposited back on the plates?
The other question would be how long is the restored battery life? Will you get another year out of it before having to do it again or will you get closer to original life?
The risk you would be taking would be permanent damage to the negative plate, as it expands and fills with lead oxide.
If you are playing with an already dead and rejected battery, in my book there is no risk. Nothing to loose, something to gain.
I have played with a lot of batterys as well. Boiled them up, had them gassing wildy and of course blown them up. 3 times now and I have had the acid to the face.
Every single time I have blown a battery, it was NOT doing anything I should not have been, just charging them ( or not) normally. First one that went off I was about 20. Had taken the battery out of the car and sat it under the workbench. I dropped a shifter which landed right across the terminals. Must have been some gas venting because the entire top of the thing went straight up followed but a rush of acid. I had looked down to see the shifter fall but managed to close my eyes maybe in reaction to the sound before the acid got me. Run for the garden hose, Clothes ruined like a swiss cheese, I was OK.
Next one was charging a battery with the caps off and again managed to drop something that hit one of the clamps on the terminal and knocked it off. Must have sparked and whooshka. Blew the thing to pieces. Saw the bit of metal falling and turned away before it hit but was nearly deaf for about 3 days.
Last one was about 2 years ago. Had a battery from my 4WD which was a very large and quite new one on charge as I replaced the alternator. I'm pretty sure that must have been faulty. Was no where near charged and only on a 2.5A charger. I had it sitting on the ground down from where I was standing, ( had just walked up to the bench with something) when the thing again blew apart like a bomb. Scared the crap out of me because I had not touched the thing or come within about 3 ft of it. Daughter was sitting on the back verandah and looked up in time to see me throw myself into the swimming pool in the middle of winter fully clothed and stay down a long time.
I caught a piece of plastic in my leg which I didn't even feel till my daughter pointed out as I was trying to get my jacket off. The blood was running down my leg quite well. Pulled the plastic out and then it hurt like a bitch. It slowed bleeding in the shower but was a nice deep 2" gash. Bandaged it up and it was fine apart from the pain. Don't like stitches.
Just annoys the crap out of me that every time I get hurt, it's innocent. I do all manner of stupid $#|+ where I am expecting to get my butt smacked by the hand of the " You should not have been doing something so stupid or dangerous" god but nothing EVER happens. Come out the shower in the lounge room where mrs throws me a t Shirt from the washing she is sorting and nearly loose a thumb as I pull it over my head and stick my hand in the ceiling fan. Play with an induction generator doing 500V+ and work on live terminals, nothing. Finish up and walk out the shed looking at something and knock myself out on the roller door I didn't push up far enough and wake up 5 min later looking at the sky and wondering how I got flat on my back on the floor?
If I got hurt Boiling batterys or playing with DIY burners doing 600KW and throwing 8ft flames I'd say Fair enough, serves myself right but it's always something like slipping on wet grass and doing my knee a month ago ( that still hurts like hell) where I has hobbling for a week that is what gets me.
I just moved here and cashed in a heap of dead batterys. I'll have to give this a go next time I get one. Think the battery in the ute is getting a bit ordinary so that may be the first test.
Question I have though is how can you tell a battery is sulphated or when it's died from other causes and what apart from internal shorting and breaks in the connections can there be?
I think I'll charge the batterys in a wooden crate on it's side with the open side facing a wall or into the yard. The crate would then be completely ventilated and act like a blast shield should another want to become a firework on me. Of course the fact I would be doing something risky would also mean nothing will happen to it at all.