State of Charge

Battle River Solar Products

	Serving Central Alberta

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	Battery State of Charge

Temperature Effect

The power available from your battery is greatly affected by its ambient temperature. The chart below illustrates this.

27ºC (80ºF) 100%

0ºC (32ºF) 65%

-18ºC (0ºF) 40%

Specific Gravity

There are several methods to check the state of charge of a lead acid battery. One way is to check the specific gravity of the electrolyte. Specific gravity is the weight of a given volume of liquid divided by the weight of an equal volume of water. The chart below gives the specific gravity of electrolyte at various states of charge.

Specific Gravity	State of Charge	Open Circuit Voltage
1.265	100%	12.60
1.245	90%	12.57
1.230	80%	12.54
1.216	70%	12.45
1.202	60%	12.36
1.190	50%	12.27
1.175	40%	12.18
1.160	30%	12.09
1.148	20%	12.00
1.120	Dead	Dead

These values may vary slightly, according to the design factors of a particular battery. Specific gravity measurements are based on a standard temperature of 27ºc (80ºF). That is:

	For every 10ºF above 80ºF, add 0.004 to the specific gravity reading.
	For every 10ºF bellow 80ºF, subtract 0.004 to the specific gravity reading.