TECHNICAL NEWSLETTER Edition 13 - September 2015
THE INFLUENCE OF TEMPERATURE ON LEAD-ACID BATTERIES Rather like human beings, lead-acid batteries react to temperature change. But while humans can respond by wearing more or less clothing, a battery is unprotected against fluctuations in temperature from -30°C to +60°C and above. As a rule, chemical reactions take place faster in warm temperatures and the battery disposes over its full performance capacity. Nevertheless, once the thermometer passes the 30°C mark, the battery reacts as we humans do and starts to sweat. Water consumption rises rapidly and grid corrosion accelerates. In fact, if a battery is exposed to high temperatures over a prolonged period, grid corrosion accelerates leading to a steady loss of conductivity. And in a worst-case scenario, corrosion advances to a point at which function ceases completely. Moreover, on rare occasions grid growth is so extensive that this results in a connector short circuit (see Illustration 1).
Illustration 1. Connector short circuit due to grid growth The effects of temperature on storage In line with a fundamental chemical principle, battery self-discharge doubles when the temperature rises by around 10°C. Higher temperatures also mean shorter suitability for storage and briefer recharging intervals. Illustration 2 shows the self-discharge curve for a variety of temperatures and once 12.50V is reached, a battery must be recharged immediately in order to prevent irreparable damage caused by advanced sulphation.
Illustration 2. Self-discharge curve
Because warm air rises, the Inuit always build the entrances to their igloos at the lowest possible point and the same principle must apply to battery warehousing. For as compared to other automotive components, a battery is certainly the most temperature-sensitive and should always be stored as close to ground level as possible. People become thirstier in the heat and so do batteries! Accordingly, during operations under extreme conditions in desert and tropical regions, even maintenance-free batteries such as the Buffalo Bull SHD and SHD PRO are refilled regularly with distilled or demineralised water (DIN 43530) in order to compensate for temperature impact. Performance capacity versus power requirement Internal engine abrasion declines in warmer temperatures. Combustion is also more efficient, oil is less viscose and the power requirement is correspondingly smaller. However, with falling temperatures the power needs of the engine rise. Conversely, the power capacity of the battery decreases in low temperatures (see Illustration 3). Therefore, the further the temperature drops, the wider the gap between battery capacity and the engine’s power requirement becomes (see Illustration 4).
Banner GmbH, A-4021 Linz-Austria, Postfach 777, Banner Straße 1, Tel. +43/(0)732/38 88-0, Telefax Sales +43/(0)732/38 88-21599, e-mail: office@bannerbatterien.com Author: Thomas Langthaler, Marketing
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Illustration 4. Starting power requirement of the engine as compared to battery performance capacity Consequently, the largest amount of starting power is needed when the battery is at its lowest performance level! When the temperature of the battery drops below freezing point, charge intake becomes markedly poorer. Charge acceptance also declines significantly in line with falls in temperature. As a consequence, in spite of regular drives the battery is not, or only insufficiently, recharged. The POS bears a major responsibility. By means of correct storage and special advice that corresponds with the area of application, specialist retailers and workshops can contribute significantly to either a minimisation of negative temperature influences, or the appropriate counteraction.