# How can I measure my battery's “State of Charge”?

If the battery's temperature, or electrolyte in flooded types, is above 110° F (43.3° C), allow it to cool. To determine the battery's state of charge with the battery's temperature at 80° F (26.7° C), use the following tables. Table 1 assumes that a 12.65 voltage reading or a 1.265 specific gravity reading represents a fully charged battery. For other battery or electrolyte temperatures, use the Temperature Compensation tables below to adjust the Open Circuit Voltage for VRLA DRY CELL batteries or Specific Gravity readings for flooded types.

Table 6 - Electrolyte Freezing Point

 Digital Voltmeter State of Charge Hydrometer Reading Electrolyte Open Circuit Volts Approximate Specific Gravity Freezing Point 12.65 100% 1.265 -75° F (-59.4° C) 12.45 75% 1.225 -55° F (-48.3° C) 12.24 50% 1.190 -34° F (-36.7° C) 12.06 25% 1.155 -16° F (-26.7° C) 11.89 Discharged 1.120 -10° F (-23.3° C)

Table 7 - Hydrometer Temperature Compensation

 Temperature Add or Subtract to Hydrometer Reading Add or Subtract to Voltmeter Reading 0° / -17.8° -.032 -.192 10° / -12.2° -.028 -.168 20° / -6.7° -.024 -.144 30° / -1.1° -.020 -.120 40° / 4.4° -.016 -.096 50° / 10° -.012 -.072 60° / 15.6° -.008 -.048 70° / 21.1° -.004 -.024 80° / 26.7° 0 0 90° / 32.2° +.004 +.024 100° / 37.8° +.008 +.048 110° / 43.3° +.012 +.072 120° / 48.9° +.016 +.096 130° / 54.4° +.020 +.120 140° / 60.0° +.024 +.144 150° / 65.6° +.028 +.168 160° / 71.1° +.032 +.192

Table 8 - Voltmeter Temperature Compensation

 Temperature Add or Subtract to Hydrometers Reading Add or Subtract to Voltmeter Reading 0° / -17.8° -.032 -.192 10° / -12.2° -.028 -.168 20° / -6.7° -.024 -.144 30° / -1.1° -.020 -.120 40° / 4.4° -.016 -.096 50° / 10° -.012 -.072 60° / 15.6° -.008 -.048 70° / 21.1° -.004 -.024 80° / 26.7° 0 0 90° / 32.2° +.004 +.024 100° / 37.8° +.008 +.048 110° / 43.3° +.012 +.072 120° / 48.9° +.016 +.096 130° / 54.4° +.020 +.120 140° / 60.0° +.024 +.144 150° / 65.6° +.028 +.168 160° / 71.1° +.032 +.192