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11.1. Protecting your car battery from high underhood temperatures with a heat shield or case, keeping it full charged at all times, and maintaining it are the easiest ways to extend it's life. In hot climates and during summer, the electrolyte levels need to be checked more frequently. In a study conducted by the Society of Automotive Engineers (SAE), the underhood temperature has increased more than 30% since 1985. For every increase of 18° F (10° C) above 77° F (25° C), positive grid corrosion or self-discharge rate is doubled.

Chrysler studies have shown that relocating the battery outside the engine compartment has increased the average OEM battery life by eight months. Relocating the starting battery to the trunk or passenger compartment, as Mazda did in their Miata a number of years ago, is becoming more popular by the car manufacturers to protect the starting battery from the high underhood temperatures. However, use sealed AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA type batteries because they normally do not produce gas when recharged or use wet batteries vented to the outside. If you use a Gel Cell (Ca/Ca) VRLA as a starting battery, you might have to lower the charging system voltages because they are very critical and to keep from overcharging the battery.

For motive and stationary deep cycle batteries, temperature is equally as important for extending the service life of the battery or battery bank. Common sense and chemical intuition suggest that the higher the temperature, the faster a given chemical reaction will proceed. Quantitatively this relationship between the rate a chemical reaction proceeds and its temperature is determined by the Arrhenius equation. Battery life, due to positive grid corrosion, is reduced by 50% for every 18° F (10° C) rise in ambient temperature over 77° F (25° C).