Ambient Temperatures Affect VRLA Batteries Service Life
There are a series of factors that directly affect VRLA reliability and service life. Other papers have addressed these in detail so we will touch upon only the major factors here. Heat is perhaps the single biggest enemy of stationary lead acid batteries. Depending upon manufacturer & product, expected life of all lead acid batteries will be cut in half for every 10-15 degree (F) rise in temperature over recommendation (usually 77 degrees F). For VRLA types, impact of excessive heat is most severe because it will lead to dry-out and open circuit failure, and in worst case scenarios in combination with older chargers, can contribute to thermal runaway, with explosive results.
The effects of temperature on valve-regulated lead-acid (VRLA) battery performance are quantified for the following areas:
(1) The capacity-temperature relationship (dC/dT) for discharge rates of 0.17 to 8.0 hours and a temperature range of 30 to 140°F (-1 to 60°C); (2) empirical equations are derived to allow the calculation of dC/dT for most discharge rates;
(3) The external surface temperature which best tracks the cell internal temperature during discharge was found to be the container wall surface, parallel to the plates;
(4) Tests in which the -3 mV/°C coefficient is applied to prevent thermal runaway are shown to cause negative plate self-discharge at temperatures as low as 37°C (99°F);
(5) A container wall surface temperature was found to be within 2°C of the internal cell in lift: tests at 50°C (122°F);
(6) Experimental results indicated that cell failure due to negative plate self-discharge at 25°C may not be detected in elevated ambient or life test temperatures.
The optimum temperature for a VRLA battery, upon which most manufacturers’ warranties are based, is 77℉（25℃）. For a battery maintained at constant charge, there is a 50% reduction in life expectancy for every 15℉ increase in ambient temperature above 77℉. The batteries must also be installed with the proper spacing per the manufacturers’ recommendations in order to maintain the necessary ventilation
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