Specific gravity refers to the state-of charge of the battery. The higher the specific gravity, the more charged the battery is. Specific gravity actually measures the concentration of the acid, so depending on when measurements are made, specific gravity’s will give differing values.
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All that said, there will be deterioration of active material on the positive plates of the battery over time. This is normal. The greater the deterioration, the lower the SG of the battery when in its fully charged state. An older battery clean of sulfate crystals will always show a lower SG than that of a new one.

Instead of measuring specific gravity, it’s actually more accurate to measure the CCA (Cold Cranking Amps) of the battery. After all, you don’t need to know how charged your battery is. You want to know how well it’ll crank your vehicle. Specific gravity is actually a poor indicator of the battery’s performance as it changes depending of the state of charge of the battery, and it doesn’t actually tell you how much more lifespan you have left in your battery.

Also, max specific gravity depends on the battery itself. For example, certain batteries only have a max specific gravity of 1.255 – 1.260. Maintenance-Free batteries can go up to 1.280.

Uneven SG between cells just mean that some cells are more charged than others. Never pour out the electrolyte. The battery is a balanced CLOSED environment, and the only thing you ever add to it is distilled water.
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To get the cells equalized, you can either connect the battery to a charger and desulfator and leave it for a few days, or simply overcharge (at a higher voltage) for an hour or so (you’ll see lots of gassing in the electrolyte).

Leave the desulfator connected to the battery at all times. That’s when it works best. The car’s electronics will not disrupt the efficacy of the Desulfator.

Operation-wise, there’s hardly any difference between 12.95 or 12.50 or 13.50V. The key point here is that the desulfator works when “the engine is on” and turns itself before the battery gets discharged. The electronics that make up the desulfator are analogue based, and there will be a slight tolerance between units. In this case, it’s less than 4%. It’s not a failure or defect, and will work fine. So they are not faulty.

Batteries failures are usually due to several factors:

• Natural wear & tear: old age, separators between plates decay, plate connectors corrode, etc.
• Abuse – filling tap water instead of distilled water into the batteries.
• Lack of Maintenance – not filling water into the batteries, loose connectors.
• Ageing – batteries that are too aged will lose active material.
• Crystallisation of Lead Sulfate – 84% of batteries fail due to this (Battery Council International).

As the names suggests, desulfators can only recover sulfated batteries that are not too aged.