Battery Hydrometer Temperature Correction

Battery Hydrometer Readings Chart – Temperature Correction

Hydrometer Temperature Correction

The temperature correction table below is one way to account for the drastic variations in specific gravity readings at various temperatures.

To use this chart, you will need to know the temperature of the electrolyte.  If measuring electrolyte temperature is impractical, you can use the temperature of the ambient air provided that you have allowed your battery sufficient time to “soak” in the environment while disconnected.

Temp Deg F
State of Charge
1007550250
01.2971.2571.2221.1871.152
101.2931.2531.2181.1831.148
201.2891.2491.2141.1791.144
301.2851.2451.2101.1751.140
401.2811.2411.2061.1711.136
501.2771.2371.2021.1671.132
601.2731.2331.1981.1631.128
701.2691.2291.1941.1591.124
801.2651.2251.1901.1551.120
901.2611.2211.1861.1511.116
1001.2571.2171.1821.1471.112
1101.2531.2131.1781.1431.108
1201.2491.2091.1741.1391.104
1301.2451.2051.1701.1351.100
1401.2411.2011.1661.1311.006

Battery Hydrometer Correction by Addition and Subtraction

Another way to make corrections is to simply add or subtract 0.004 to your reading for every ten degrees of difference between 80 degrees and your actual temperature.  The result will provide you a hydrometer reading when not using a temperature compensated hydrometer.

Subtract 0.004 for every ten degrees when the temperature is below 80

Add 0.004 for every ten degrees when the temperature is above 80

Example 1

  1. Your hydrometer reads 1.233
  2. Its 60 degrees F
  3. It is 20 degree below 80.
  4. You subtract 0.008 from 1.233
  5. The result is 1.225, thus the state of charge is approximately 75 percent.

Example 2

  1. Your hydrometer reads 1.178
  2. Its 110 degrees F
  3. It is 30 degree above 80.
  4. You add 0.012 to 1.178
  5. The result is 1.190, thus the state of charge is approximately 50 percent.

Battery SOC and Specific Gravity

State of ChargeSpecific Gravity
100%1.265
75%1.225
50%1.190
25%1.155
0%1.120

Downloadable PDF: Hydrometer Temperature Correction