Battery malfunction is seldom caused by a factory defect; driving habits are the more common culprits. Heavy accessory power when driving short distance prevents a periodic fully saturated charge that is so important for the longevity of a lead acid battery. According to a leading European manufacturer of car batteries, factory defects amounts to less than 7 percent. The battery remains a weak link and the breakdowns on 1.95 million vehicles six years or less are as follows: 52% battery 15% flat tire 8% engine 7% wheels 7% fuel injection 6% heating & cooling 6% fuel system A breakdown due to the battery remains the number one cause. * Source ADAC 2008 for the year 2007 Acid stratification, a problem with luxury cars A common cause of battery failure is acid stratification. The electrolyte on a stratified battery concentrates on the bottom, causing the upper half of the cell to be acid poor. This effect is similar to a cup of coffee in which the sugar collects on the bottom when the waitress forgets to bring the stirring spoon. Batteries tend to stratify if kept at low charge (below 80%) and never have the opportunity to receive a full charge. Short distance driving while running windshield wiper and electric heaters contributes to this. Acid stratification reduces the overall performance of the battery. Figure 1 illustrates a normal battery in which the acid is equally distributed form top to bottom. This battery provides good performance because the correct acid concentration surrounds the plates. Figure 2 shows a stratified battery in which the acid concentration is light on top and heavy on the bottom. A light acid limits plate activation, promotes corrosion and reduces performance. High acid concentration on the bottom, on the other hand, artificially raises the open circuit voltage. The battery appears fully charged but provides a low CCA. High acid concentration also promotes sulfation and decreases the already low conductivity further. If unchecked, such a condition will eventually lead to battery failure.

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