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Effect of temperature

Briefly, electrolyte temperature above 77°F (25°C) will result in a lower observed gravity reading approximately equal to a loss of 1 point (0.001) for each 3°F (1.67°C). In contrast electrolyte below 77°F (25°C) will read approximately 1 point (0.001) higher for each 3°F (1.67°C). Higher temperatures expand the volume of electrolyte which reduces the observed specific gravity, while lower temperatures condense the electrolyte and thereby concentrates the electrolyte.

The lead acid battery is an electrochemical device. Heat accelerates chemical activity; cold slows it down. Normal battery operating temperature is considered to be 77°F (25°C). Higher-than-normal temperature has the following effects on a lead acid battery:

• Increases performance
• Increases internal discharge or local action losses
• Lowers cell voltage for a given charge current
• Raises charging current for a given charge voltage
• Shortens life
• Increases water usage
• Increases maintenance requirements

Lower than normal temperatures have the opposite effects. In general, at recommended float voltage, a battery in a cool location will last longer and require less maintenance than one in a warm location.

If the operating temperature is something other than 77°F (25°C), it is desirable to modify the float voltage as follows: For temperatures other than 77°F (25°C), correct float voltage by 2.8 mV/°F (5.0 mV/°C). Add 2.8 mV (0.0028 Volt) per °F (5.0 mV/°C) below 77°F (25°C).

Subtract 2.8 mV (0.0028 Volts) per °F (5.0 mV/°C) above 77°F (25°C).

Example: C&D Model LCT 1680
Nominal float @ 77°F is 2.20 Vpc Corrected float @ 67°F is 2.228 Vpc Corrected float @ 87°F is 2.172 Vpc

At higher than normal operating temperatures, for every additional 15°F (8°C) battery life is decreased by 50 percent. Therefore, continued operation at an average cell temperature of 92°F (33°C) will reduce battery life to 50 percent of that typical at 77°F (25°C).