Unless you keep them on trickle charge for the winter months, (or recharge every month) batteries on classic cars that are driven sparingly do not last long. I found a 7 year old (dated) 12 V Everstart (Walmart) battery in my garage tucked away in the corner that has been sitting untouched for at least 6 years. Put the meter on it and it measured zero volts. Tried a couple of chargers including the Optima, Viking, Shauer 10 amp and the needles on them would not move and the battery would not take a charge. Finally I got out the old Schauer 4 AMP charger and connected it but this time I attached a $20 battery Desulfator that I purchased on eBay across the terminals. Let it sit for two hours and sure enough the meter on the charger showed that it was now charging. Kept it connected for two more hours, disconnected everything and the battery now measured 12 Volts. Then I put it on the big charger and put it at the 60 amp setting for 20 minutes. The charge then read full at 12.8 Volts. Tested the following day and the battery was holding that charge. Put it on a car and it started right up. This obviously can't fix a battery with internal damage or one full of worn plate grit but it can work some of the time. I now have an old battery that is useful and it saved me $80

This is what I used

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: I got out the old Schauer 4 AMP charger and connected it but this time I attached a $20 battery Desulfator that I purchased on eBay across the terminals. Let it sit for two hours and sure enough the meter on the charger showed that it was now charging.

Just so this is clear... this Battery Desulfator is connected to a car battery at the same time as a separate battery charger?

Something like this.
https://www.amazon.com/clea...hy=&hvtargid=pla-458 4345015837047&psc=1

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

quote Originally posted by Patrick: Just so this is clear... this Battery Desulfator is connected to a car battery at the same time as a separate battery charger?

Initially the desulfator was attached across the terminals with a old non solid state 4 amp battery charger. Then after an hour the battery came alive as the needle on the charger was now moving half way. I left that combo for a couple of hours and the voltage came up to about 12 volts, I disconnected the charger and left the desulfator connected. The first day after 24 hours on the desulfater the battery read 12.2 Volts that is about a 25% charge. Again added the small charger and the desulfator connected for an hour and then just the desulfator for another 24 hours. The battery voltage was now 12.26 volts which is 50% charge. Put it now on the big charger for 20 minutes and the battery voltage read 12.45 volts which is about a 75% charge and that's where it stood. Tried it and the car started right up.
Here are the voltage ranges for the battery charge, tested when standing an un-connected
11.75V-11.89V battery is dead
11.99V-12.06 V is a 25% charge
12.24-12.29 V is a 50% charge
12.45-12.54 V is a 75% charge
12.65-12.77 V is a Full Charge
At this point I do not know if the old battery will reach full charge until I run it on the road for a while but it still satisfying to have revived a dead battery that was sitting uncharged for so long and have it start the vehicle again. The desulfation process will not work on all dead batteries as they can deteriorate internally but if you have a good battery in storage that sat unused for a long time this process may work. The tip that I can pass on is to start the charging process slowly, monitor voltages and keep the desulfator on for 48 hours total.
UPDATE 3/25/2:45 PM. Kept it on the battery Defulfator again over night, w no charger attached. Charged for 90 minutes this morning on the 10 amp Exide charger and am now at 12.59 volts -75% charge. I am pleasantly surprised at the results restoring this old battery. Expect to be at 12.65 volts tomorrow for 100% charge.

A couple of more notes. The Optima and the Viking battery chargers/maintainers/restorers/desulfators did not work. Only the low cost $20.00 "Clean Power" unit purchased on eBay did in conjunction with old style non-solid state battery chargers. I used both the 10 amp Exide and the 4 amp Schauer units for this experiment. Start by trying to charge with the battery charger and Desulfator connected .Then just connect the desulfator overnight then charge again.
UPDATE 3/27/21- Voltage readings on this old battery are now 12.8V -100% ful charge. It took a few cycles of 4 a charge w desulfator, then Desulfator alone, then charge again, desulfate again. Took three days to get this battery back to like new performance. Best $20 I ever spent.
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 03-27-2021).]