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 readings therefore will give differing values.

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.

A more accurate diagnosis of your battery health

Instead of measuring specific gravity, it's actually more accurate to measure the cold cranking amps (CCA) of the battery. After all, you don't need to know how charged your battery is. You want to know how well it will 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.

What is CCA or cold cranking amps?

Cold Cranking Amps is a rating used in the battery industry to define a battery's ability to start an engine in cold temperatures. The rating is the number of amps a new, fully charged battery can deliver at 0° Farenheit for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. The higher the CCA rating, the greater the starting power of the battery

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