Common Causes of Battery Failure

The battery is not designed to last indefinitely, however, with proper care, it will provide many years of service. If the battery passes a load test but the vehicle still exhibits a slow cranking or a discharged battery condition, the following are some of the more common conditions that may be the cause of the trouble:
^ Vehicle accessories left on overnight.
^ Slow average driving speeds for short periods, so the battery does not have sufficient time to recharge.
^ The vehicle's electrical load is more than the generator output. This is more likely with the addition of aftermarket equipment.
^ Fault conditions in the charging system such as a high resistance in the ground circuits, electrical shorts, a slipping drive belt, or a faulty generator or voltage regulator.
^ Battery abuse, including failure to keep the battery cable terminals clean and tight, or a loose battery hold down retainer.
^ Mechanical conditions in the electrical system, such as shorted or pinched wires.
^ Extended storage of vehicles.
^ Replacement battery not having sufficient charge when installed in the vehicle.
^ Extended engine cranking due to a possible vehicle fuel or ignition system problem.
^ Incorrect interpretation of the battery's built-in hydrometer.

In addition, a certain amount of self-discharge is always occurring as a result of internal chemical reactions, even when the battery is not connected. This explains why the number of discharged batteries in stored vehicles may increase in very hot weather.