When it comes to vehicle maintenance, “normal” is determined by a number of factors that exist in theory but rarely occur. A battery, for example, has an average lifespan of four years under normal conditions. A “normal” battery is one that goes through full charge cycles, is not subjected to extreme temperatures, is charged on a reliable and consistent system, and doesn’t provide power for a lot of accessories.
Normal just isn’t normal. Temperature extremes, vibration, short trips down the street, and an ever-increasing assortment of smartphones, aftermarket navigation systems, and other devices all drain the battery.
This makes sense when you consider a typical maintenance-free lead-acid car battery. The plastic box contains lead plates and lead dioxide plates. An electrolytic solution is formed by suspending the plates in a mixture of water and sulfuric acid. By allowing electrons to flow between the plates, electricity is created.
There are many factors that can disrupt this chemical reaction. A poorly-secured battery or rough travel can shake loose or damage the plates. Extreme heat speeds up chemical reactions, shortening battery life, while extreme cold slows down chemical reactions, extending battery life. To keep extreme temperatures under control, some batteries are covered with an insulating sleeve.
Driving style can also affect the reaction. When the car is started, it consumes a lot of energy, so the charging system has to step in to replenish the battery. As a result, if you have a short commute or take lots of short trips, the battery will never be fully charged. This constant undercharging leads to acid stratification.
Electrolyte solution inside the battery changes from homogenous – or the same all the way through – to a rough vertical split. The upper half of the solution is a light acid, and the bottom is a heavy acid. The light acid layer will begin to corrode the plates and the heavy acid solution will start compensating for the car’s electrical needs by working harder than it was designed to. Even though the battery appears to work on routine tests, it has a shorter life.