Battery Data - Voltage and Specific Gravity

Dave and Helen Damouth www.damouth.com

9 Nov. 2001

The following data is for flooded cell lead-acid batteries at 77° F. 
Battery Voltage will rise .02 V. for each 10° F. drop in temperature,
and vice versa.  Other types of battery will differ slightly.

Charge level
(percent of
full charge)		 12v. battery voltage Volts per Cell Specific Gravity
100 12.64 2.106 1.265*
90 12.55 2.091 1.251
80 12.46 2.076 1.236
70 12.37 2.061 1.221
60 12.28 2.046 1.206
50 12.18 2.031 1.191
40 12.10 2.016 1.176
30 12.00 2.001 1.161
20 11.92 1.986 1.146
0 11.83 1.971 1.131

Caution: 

  1. After battery charging, the voltage will read abnormally high until battery has been disconnected from charging source and rested for many hours, preferably overnight.
  2. While battery is discharging, voltage will read abnormally low.  Disconnect battery from all loads before measuring.
  3. Inexpensive multimeters may have errors of several percent, making them almost useless for reading battery voltage.  The difference between 50% and 80% charge level is only a little over 2%.  I suggest spending the additional money for a meter rated for 0.1% voltage accuracy.
  4. Some references say that golf cart batteries have a slightly higher acid contest, with a specific gravity of 1.275 at full charge.
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