A flat, or discharged, battery can be a real pain when you go to start your car in the morning before work. As aggravating as this can be, there are additional issues to consider when dealing with a car that has a battery that is not properly holding a charge.
- The alternator charges the battery and continues to try to charge the battery while the car is running. If the voltage level does not reach an acceptable amount, normally around 12 volts, the alternator may run non-stop during your entire drive. Since the alternator is linked directly to the drive or accessory belt that is turned by your engine, the added resistance of the alternator working can cause a slight decrease in fuel economy. In reality, this decrease would be too small for most people to realize. However, the life of the alternator could be shortened.
- Without a properly charged battery, the fuel injectors may not add fuel to the cylinders as efficiently as they normally would. This has the potential to cause more loss of fuel mileage than the alternator simply running all of the time. You may notice the engine lurching or the car seeming to run a little rough. This is sometimes an indication that a quick check of the battery is in order.
- The car’s computer will normally continue acceptable operation, but other accessories will provide additional load on the car’s electrical and mechanical system. The oxygen sensor and other exhaust gas sensors may not work well on a lower voltage than recommended by the manufacturer. In this event, the computer will be unable to accurately gauge whether fuel consumption matches the rate of exhaust produced. Without this capability, more fuel may be used and lost through the exhaust.
- Some cars are equipped with the ability to shut off some of the cylinders in the engine during low-intensity operation, such as driving in a city at low speeds. Some large cars have this ability, but it is dependent upon the computer and other systems knowing when to shut the cylinders down for maximum fuel conservation. If the computer is unable to gain the important electrical information it needs from the multitude of sensors in the car, it will not be able to shut the cylinders down. There will be a marked loss of efficiency due to the loss of such an option.