I have some brand new lead-acid batteries that have never been used. They have been stored in my garage for a while (1-1/2 to 2 yrs). My smart charger errors and won’t charge them. Why is this and is there anything that can be done to revive them?
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Most smart chargers are designed to not put out current if the voltage on the load is too low. This protects the charger against short circuits and any load that isn’t a short but would overheat the charger.
Batteries that have sat that long may or may not be rescuable. The best thing to try is a “dumb” charger with external current limiting. For a car battery, the external current limiter can be a sealed beam or H4 halogen headlamp bulb; the charger should be 6 amp or bigger. For motorcycle batteries, the same rig but with a tail lamp bulb.
Once the battery has some voltage on it, you can switch over to the smart charger. If the battery voltage is above the smart charger’s go/no go threshold, it will charge the battery. A field expedient to the dumb charger and bulb limiter is to use another battery of the same voltage which has charge in it, plus the bulb limiter, across the discharged battery to bring its voltage up. A rescuable battery will have the bulb glow brightly and then gradually dim as the dead battery voltage rises.
Lead acid (PbA) batteries have a high self discharge rate. They will go dead just sitting. They also have a short calendar life, more than 3 years old you can expect to have problems. A smart charger will see the voltage is to low and abort charging. The longer the cell voltage remains below 1.5V the more damage is done shortening their life and capacity. To extend PbA battery life requires a float charger like the 'Battery Tender'.
From the 1.5 to 2 years of storage mentioned I'd say you now have paper weights. A slow trickle charge done with a bench power supply at a low current to about 2V per cell, may bring them up. But how useful they'll be remains to be seen. Then you can hook up your smart charger and see what happens. Don't leave the charging unattended, you can stop it over night by disconnecting one terminal. Some power supplies can be back fed from the battery when turned off. You have to watch out with batteries of unknown condition. Fires can happen. This applies to PbA as well as lithium based batteries. An alarm is useless when there's no one around to take action.