How to Troubleshoot the Battery Running Down in My Car

Where is the problem?

All of us have had the unpleasant experience of being stuck somewhere because of a dead battery. Always keep a pair of jumper cables in your trunk. These will usually get you from point A to point B. However, you still need to figure out what caused the problem. Jumper cables offer little assistance for batteries that are old and worn. In diagnosing why a battery keeps running down there are four options; 1) you left the lights on; 2) the battery is bad, 3) there is a problem with the charging system, or 4) there is an electrical problem.

Things You'll Need

• voltmeter
• ammeter

Instructions

Introduction

1. Look for the obvious. Diagnosing a drained battery can be as simple as checking to see if you left the headlights or the radio on. Also inspect the battery cables and terminals for corrosion. Corrosion is natural occurrence in metals. The electrochemical oxidation of metals reacts to the natural environment. This will cause metals to degrade overtime. Corrosion will interfere with the battery. It can be cleaned with a wire brush. Another option is to spray the terminals and cables with anti-corrosion spray and let it sit for a few minutes. Then simply rinse it off.

2. Check the battery's ability to hold a charge. New batteries have a lifespan between 5 to 6 years. As they age they become weaker and eventually are unable to hold a charge. One way of checking your battery is to recharge it, disconnect the cables and let it sit overnight. Reconnect the cables and try to start the car. If the battery holds its charge then the source of the problem is not the battery.

3. Investigate the charging system. If the problem is not the battery itself then it may be that the alternator is not recharging the battery.There are two ways to do this. Start the car and turn the headlights on. If the headlights are dim this indicates that the lights are running off of the battery. The alternator is producing little or no power. You can also check the alternator with a voltmeter. Connect the red positive test lead of the voltmeter to the positive terminal of the battery. Connect the negative test lead the the negative terminal of the battery. The voltmeter should register 14.5 volts with the engine turned on.

4. Inspect the electrical system. If the battery and charging system functioning properly the only option left is the electrical system. Something is causing the battery to drain while the car is turned off. The source of the problem could be any part of the electrical system from a bad wire to frozen fuel pump relay switch. Use an ammeter to try to locate the problem. Disconnect one of the battery cables. Connect one ammeter lead to the cable and the other lead to the battery terminal. The ammeter should read 25 milliamps with the ignition in the off position. If it is reading around 100 milliamps this indicates an electrical problem. There is something stuck in the on position. The next step is to begin removing fuses till the ammeter drops to 25 milliamps. This will tell you where the problem is.

References

• Autofacts: A Dead Car Battery
• Aa1car: Diagnosing an Engine that won't start