How do I temperature compensate my voltmeter readings?

If you are using a digital voltmeter make the adjustments indicated in the table above. For example, at 30° F (-1.1˚ C), the voltage reading would be 12.53 for a 100% State-of-Charge. At 100˚ F (37.8˚ C), the voltage would be 12.698 for 100% State-of-Charge. For sealed batteries, measure the Open Circuit Voltage across the battery terminals with an accurate digital voltmeter. This is the only way you can determine the State-of-Charge on sealed flooded or VRLA batteries. Some sealed flooded batteries have a built-in hydrometer, which only measures the State-of-Charge in one of its cells. If the built-in indicator is clear or light yellow, then the battery has a low electrolyte level and needs to be replaced. If the State-of-Charge is 75% using either the specific gravity or voltage test or the built-in hydrometer indicates “bad” (usually dark), then the battery needs to be recharged.