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When a battery is being charged, you will get a higher voltage reading than you would find at rest. Most renewable energy charging systems will charge a battery until the battery reaches 14.5 volts and then will automatically shut off. The battery voltage will drop slowly. The most accurate way to check the true charge state of a battery is with a hydrometer. A specific gravity of 1.260 in a lead acid battery means it is fully charged. As a battery discharges it will fall to 1.120 when discharged. The ratings are at 77F. If the temperature is lower than 77F then the specific gravity will be inflated. Premium hydrometers will have a temperature and give you a compensation factor.

Correction factors:
130 degrees F+0020
120 degrees F +0016
110 degrees F+0012
100 degrees F+0008
90 degrees F+0004
80 degrees F0000
70 degrees F-0004
60 degrees F-0008
50 degrees F-0012
40 degrees F-0016
30 degrees F-0020
Percent charge Voltage
100% 12.60
25% 11.95
discharged 11.85 or below

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