Battery Voltmeter Readings Chart – Temperature Correction
Properly measuring the Battery State of Charge using a voltmeter requires that the measurement be adjusted for the temperature. The chart below will help you do just that.
To use this chart, you will need to know the temperature of the battery terminal. Alternately, you can measure the temperature of the air around the battery provide that the battery has had several hours to stabilize in the environment that it is in.
|Temp Deg F|
Battery Voltmeter Temperature Correction using Addition and Subtraction
In this method you use the standard State of Charge versus Volts Chart. Remembering that the battery voltage will read higher in colder weather and lower in hotter weather, you simply…
- Subtract 0.024 volts for every ten degrees F, if the temperature is below 80 degrees F.
- Add 0.024 volts for every ten degrees F, if the temperature is about 80 degrees F.
- Your voltmeter reads 1.257
- Its 30 degrees F
- It is 50 degree below 80.
- You subtract 0.12 from 1.57
- The result is 1.45, thus the state of charge is approximately 75 percent.
- Your hydrometer reads 12.012
- Its 100 degrees F
- It is 20 degree above 80.
- You add 0.048 to 12.012
- The result is 12.06, thus the state of charge is approximately 25 percent.
|12.65 Vdc||100 Percent|
|12.45 Vdc||75 Percent|
|12.24 Vdc||50 Percent|
|12.06 Vdc||25 Percent|