Car Battery

The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and 14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate.

As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle.

If you experience battery trouble, there are a couple of things you may want to check:

• Be sure the battery is tightly secured and clean. Vibration caused by an unsecured battery can affect battery life.

• The cables to the battery terminals must be clean and tightly connected. Build up of corrosive elements on the terminals can seriously weaken starting power. (Be sure the side terminals aren't over-tightened as well.)