Indications

• There are several indicators that are warnings of impending failure of a car battery. If the engine turns over slowly when started, this usually means that a cell in the battery is dead or not producing. A battery that is very low when left overnight and has a difficult time turning the motor but works fine the rest of the day signals impending battery failure. A battery that is low in water in one or more cells may soon fail.
  
  

Battery Makeup

• A battery is made up of a series of cells that produce voltage and increase the amperage. All of the cells taken collectively supply the advertised amperage. If the battery has 650 cold cranking amps, this figure is all the cells collectively. If any one of the cells wear out, the amperage drops off significantly. This is the most common type of failure. The battery will still produce the correct voltage even with the reduction in amperage.
  
  

Battery Sizes and Identifications

• Each battery will have a sticker on its top with a CCA figure, such as CCA 650. This means that the battery has the ability to put out 650 amps for 30 seconds at 0 degrees Fahrenheit. The most important designation is the RC figure on the sticker. This is the reserve capacity in terms of time that the battery can run the vehicle in case of an alternator failure. It indicates how long the battery can produce 25 amps until it drops below 10.5 volts. In an emergency such as a failed alternator, this can make all the difference in how far the vehicle can travel. The physical size and shape of the battery is identified as the group number, such as a group 35 and so on. There will be a stamped in date of manufacture on the side of the battery.
  
  

Battery Demands

• Starting a vehicle requires a lot of amperage, whereas operating a running engine takes very little amperage. Another indicator of a bad battery is having a shorted cell in the battery. In this case, the vehicle battery will be extremely low or dead in the morning or after sitting for a period of time. When the vehicle is started with the help of a jump or battery charger, and the battery is once again charged, it may seem okay for the rest of the day until it is left for a period of time. In other words, the short in one or more of the cells will drain the battery slowly over a period of time.
  
  

Checking a Battery for Servicability

• The easiest and most effective way to check a battery is with an ordinary voltmeter. Turn the voltmeter to 20 volts and put the red lead to the positive lead of the battery and the black lead to the negative terminal. The voltage should show 12.5 to 12.75 volts. If it is not in range, first check the water level in the battery and correct if necessary. Charge the battery or jump start the vehicle. Check the voltage across the battery once again with the engine running. Look to see if the alternator is working to supply the voltage and charge the battery. The voltage now should be 14.5 or very close. Now turn on the air conditioning and head lights to see if the voltage remains the same or very close. If the voltage is 13.5 or less, the alternator is bad and causing the battery to look bad as the alternator is not charging the battery. If the alternator is good, now a cell check in the battery is in order. Shut the engine down. A helper will be needed for this check. Have the helper start the engine while you pay strict attention to the voltmeter. When the starter is engaged, if the voltage drops below 10 volts it means that a cell is bad and the battery needs to be replaced.
  
  

Important Information

• The battery is similar to a glass of water. The glass, when full, has a complete charge. When the car is started it is like pouring a quarter of the water out of the glass. To refill the glass with water, the glass is placed under a faucet and fill with a slow drip. The same applies here in as much as a battery will discharge rapidly but takes a long time to recharge. The battery just starts the car and the alternator takes over and supplies all the voltage used in the car and also recharges the battery. If a car stalls and will not start again while driving down the road, or after parking, the most likely cause is failure of the alternator. When this happens, the car is running strictly on the battery. A good battery can operate a car for 30 to 40 minutes safely as long as the air conditioning and lights are off. Once the battery goes dead and the alternator does not work, charging the battery will only make it possible to move the car off the road. Remember that it will take quite some time to charge the battery to even run the vehicle for a few minutes. Jumping the engine does no good because as soon as the jumper cable is removed the battery will die again. The alternator must be replaced. Never start a vehicle with a new alternator and a dead battery. The dead battery will cause the alternator to overheat and destroy itself. Always charge the battery first.