I charged an old (5 years) 8D lead acid battery with a standard charger for 24 hours. Connected the battery tester for 10 seconds and voltage fell to about 10.8 volts. Placed the Charger/Desulphator on the battery for 48 hours and checked the voltage with the tester. After 10 seconds, it was about 12.2. Also tried on 2 other batteries. One improved significantly. The other was a "bad" battery that drops to almost 0 volts when tested, so I don't think there is any hope for it. The unit did appear to make adifference on 2 of the 3 batteries compared to using a regular charger.