loopkiller
10+ year member
PERMA-BANED
First of OP, those batteries should rest at 13.0v with a full charge. At 12.0v they are 50% depleted. They will start you car because your starter will work at lower voltages. your amps however will not operate below 10.0v (maybe even higher than that). Most AGM batteries self discharge at about 2% a month. In 36 months, you should assume that battery to be completely drained (10.5v).
When you have batteries that have not been used or charged for 3 years, they need to be charged, then discharged a few times before they will even begin to make rated power. Batteries when left dormant like that become stratified. That means that the acid in the battery is heavier than the water and it sinks to the bottom of the battery. Since there is only water in the upper portion of the battery, the lead in the upper portion of the battery can no longer produce a charge. Lead needs acid to make a charge.
The only way to fix this issue is to cycle the batteries until they get a proper mix of water and acid throughout the battery. Once you get them equalized, they should begin to hold a full charge.
The other issue you are up against is called lead sulfate. This is the by product of batteries discharging. When the lead reacts to the acid, they combine to make this gooey substance (lead sulfate). Over time (days) this substance turns into a hardened form and crystallizes. Once the lead sulfate crystallizes, that portion of the lead plate can no longer make a charge either. If this crystallized lead sulfate is thick enough, even charging the battery will not break it free from the plates.
When you have batteries that have not been used or charged for 3 years, they need to be charged, then discharged a few times before they will even begin to make rated power. Batteries when left dormant like that become stratified. That means that the acid in the battery is heavier than the water and it sinks to the bottom of the battery. Since there is only water in the upper portion of the battery, the lead in the upper portion of the battery can no longer produce a charge. Lead needs acid to make a charge.
The only way to fix this issue is to cycle the batteries until they get a proper mix of water and acid throughout the battery. Once you get them equalized, they should begin to hold a full charge.
The other issue you are up against is called lead sulfate. This is the by product of batteries discharging. When the lead reacts to the acid, they combine to make this gooey substance (lead sulfate). Over time (days) this substance turns into a hardened form and crystallizes. Once the lead sulfate crystallizes, that portion of the lead plate can no longer make a charge either. If this crystallized lead sulfate is thick enough, even charging the battery will not break it free from the plates.
