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My Car Battery Won't Hold a Charge

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

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When a car battery won't hold a charge, you may be dealing with a:

  • Faulty or worn-out battery
  • Damaged or corroded battery cable(s)
  • Battery seldom used
  • Parasitic drain
  • Charging system problem

Any of these issues can deplete your battery of the required power to fire up the engine. Unless you get a jump start, your car won't go anywhere.

The following sections will help you diagnose a faulty battery or some other potential problem preventing the battery from being charged.

Tests and Diagnostic Questions Explained Below

1. Visual Inspection
2. Battery Open-Circuit Voltage Check
3. Charging Voltage Output Test
4. Ground Circuit Voltage Drop Test
5. Power Circuit Voltage Drop Test
What If My Alternator and Battery are Good?
Are You Exceeding Your Alternator’s Capacity?
Is Your Powertrain Control Module Bad?
Is Your Battery Sulfated?

Loose, corroded or damaged battery terminals will prevent the alternator from properly charging the battery.

Loose, corroded or damaged battery terminals will prevent the alternator from properly charging the battery.

1. Visual Inspection

Before you do any diagnostics, you can do a quick visual inspection. Consider the following:

  • Make sure the battery connections are clean and tight. You may need to disconnect the cables from the posts to check for corrosion. If necessary, clean the posts and terminals using a battery brush and baking soda mixed in warm water.
  • Closely examine the battery cables for signs of damage. Broken cable wires make it difficult for the battery to deliver the necessary amps to start the engine and to recharge the battery.
  • Examine the battery cable clamps for cracks. If the clamps can't hold a tight and clean grip around the battery posts, the charging system won't be able to recharge your battery properly.
  • Most car batteries have an average service life of about four years, or three years in hot climates. If you suspect you have a worn-out battery, take it to your local auto parts store and have them test it. This test will tell you whether your battery still can accept and hold a charge. Most stores will check it for free.
  • On a battery with removable caps, verify the battery has enough electrolyte, especially if you live in a hot climate area. Running your battery without sufficient water will prevent proper battery operation and ruin it.

If necessary, continue with the following tests.

Measure battery open voltage.

Measure battery open voltage.

2. Battery Open-Circuit Voltage Check

If you haven't done it yet, check the battery open-circuit voltage. You can do this simple test using a digital multimeter.

This step helps you confirm you are using a properly charged battery during the following tests.

This step helps you confirm your battery is undercharged, and also helps you make sure you are using a properly charged battery during the following tests.

  1. Pop the hood open.
  2. Set your multimeter to read DC volts.
  3. Connect the meter's red lead to the positive post on your battery, and the meter's black lead to the battery's negative post.
  4. Your meter should read at least 12.4 volts (about 75% charge).

If your battery has less than 12.4 volts, recharge it. But make sure the electrolyte is covering the cells (on batteries with removable caps) or you may destroy the battery.

If you don't have a battery charger at home, many auto parts stores will charge a battery and run tests on it to diagnose its condition.

Whether you are dealing with a good or bad battery, it is a good idea to check the charging system as well. Sometimes, problems with the charging system can ruin an otherwise perfectly good battery.

Use a properly charged battery to do the following simple tests with your digital multimeter.

Check alternator ripple voltage.

Check alternator ripple voltage.

3. Charging Voltage Output Test

The charging system in your vehicle is designed to provide sufficient voltage to run the different electrical systems in your vehicle, while recharging the battery as necessary.

The following charging voltage output test helps you check the charging system.

Make sure to work with a fully charged battery for this test. Also, you'll need a digital multimeter.

If you are testing a Honda or Acura model, turn on the headlights or some other accessory as you conduct this test. Many of these models are equipped with a load detection circuit that activates the charging field circuit to charge the battery; if not, you'll only read battery open voltage (12.4 volts) during this test.

  1. Place your transmission in Neutral (manual) or Park (automatic).
  2. Set the emergency brakes.
  3. Pop the hood open.
  4. Ask an assistant to start the engine and set engine speed at about 1500 RPM.
  5. Measure voltage across the battery posts.
  6. Voltage should be about 1.5 to 2 volts higher than open-circuit voltage.
    • If voltage is less than 13 V immediately after starting the engine, there's a charging problem.
  7. Ask your assistant to raise engine speed to about 2000 RPM and turn on the headlights, AC, and rear window defrost or some other accessories.
  8. Measure voltage across battery posts.
    • Voltage output should be 0.5 volts higher than open-circuit voltage; otherwise, there's a charging system issue.

Consult your vehicle repair manual for charging system specifications.

If the charging system didn't pass the previous test, this doesn't necessarily indicate there's something wrong with the alternator. Excessive resistance in the circuit can prevent the charging system from doing its job. The following test helps you diagnose the circuit using your digital multimeter.

Be Careful When Testing the Charging System

Some vehicle models equipped with a heated windshield may cause the alternator to output as much as 110 AC voltage. Don’t operate this system while running the following tests.

Closely examine alternator electrical connectors and wires for corrosion and damage.

Closely examine alternator electrical connectors and wires for corrosion and damage.

Doing Voltage Drop Tests

The next two tests help you check for excessive resistance in the charging circuit.

Before you start, make sure electrical connectors (depending on your particular model) on the back of the alternator are clean, tight, and in good condition. Then get your engine ready following these steps.

Preparing your engine for the tests:

  1. Engage the parking brake.
  2. Set your transmission to Park (automatic) or neutral (manual).
  3. Start the engine and let it idle.
  4. Ask an assistant to maintain engine speed at about 2000 rpm.
  5. Switch on the high-beams, wipers, AC, and other electrical accessories.

This allows high current to flow through the circuit while running the tests.

Warning!

Keep your hands and your multimeter leads away from moving components while conducting the voltage drop tests.

Testing ground circuit side voltage drop.

Testing ground circuit side voltage drop.

4. Ground Circuit Voltage Drop Test

Too much resistance in the ground circuit can cause trouble for the charging circuit and other electrical systems. Read the above section "Doing Voltage Drop Tests."

Checking the charging system's ground path:

  1. Set your voltmeter to a low setting on the DC Volts scale.
  2. Connect your voltmeter's red lead to the alternator housing.
  3. Connect your meter's black lead to the battery negative (-) post.
  4. Check your voltmeter readout.

Your drop voltage should be between 0.3 volts and 0.5 volts.

  • If your reading is below 0.3 volts, check that the alternator is properly mounted, and the mounting bracket is clean and properly secured to the engine. Check engine grounds as well. This will ensure a good path to ground.
Testing power circuit side voltage drop.

Testing power circuit side voltage drop.

5. Power Circuit Voltage Drop Test

An excessive voltage drop on the power side of the circuit will lead to an undercharged battery. Before beginning, read the section above, "Doing Voltage Drop Tests."

  1. Set your voltmeter for a low voltage output on the DC volts scale.
  2. Connect the voltmeter's red lead to the battery post (B+) on the back of the alternator.
  3. Connect the black lead to the positive (+) battery post.
  4. Check your voltmeter readout.

Typically, drop voltage should be between 0.3 volts and 0.5 volts:

  • If your reading is below 0.3 volts, have the alternator checked to make sure it is charging.
  • If your reading is over 0.5 volts, check each connection in the power side of the circuit.

You should expect a voltage drop of about 0.1 volts or lower per connection; otherwise, check for a loose, damaged or corroded connection between the battery and the alternator.

Your repair manual will list the correct specifications for your alternator and charging system.

See the Resources section at the end of this post for more help on voltage drop tests. Also, check your repair manual.

A Manual Will Help You Do These Diagnostics and Repairs

Having the repair manual for your particular vehicle model will help you make the necessary repairs. If you don't have this manual yet, get a relatively inexpensive copy through Amazon.

Haynes manuals include:

  • Photographs
  • Systems descriptions
  • Troubleshooting guides
  • Step-by-step procedures
  • Parts location
  • Electrical diagrams
  • Maintenance schedule

Besides diagnosing and troubleshooting, you can use your manual to service the vehicle yourself, by following the maintenance schedule, and save a lot of money on unnecessary repairs in the future. So you'll recoup your small investment in a short period.

Check the serpentine belt or drive belt and tensioner for looseness, wear, and damage.

Check the serpentine belt or drive belt and tensioner for looseness, wear, and damage.

Questions to Ask If Your Alternator and Battery Are Good

So your battery, charging system circuit, and alternator passed the previous tests. What now?

There are still a few things you might want to check:

  • Missing, loose, rusted, or damaged engine ground straps.
  • Loose or worn serpentine or drive belt.
  • Faulty belt tensioner.
  • Battery parasitic drain (over 50 mA after the engine is stopped, on most late-model vehicles).

If you need help with any of these issues, consult your vehicle repair manual, and the Resources at the end of this post for diagnostic procedures.

Are You Exceeding Your Alternator's Capacity?

In recent years, alternators have increased amperage output to accommodate a higher electrical demand in newer vehicle models. Still, it is possible to overload the system by running accessories like high-amperage sound systems or pulling a trailer.

A similar situation arises when you drive short distances with high-load accessories turned on, like:

  • Cooling fan
  • Window defroster
  • Electric power steering
  • AC blower motor
  • Sound system

In this case, you are not giving the alternator a chance to recharge your battery.

Could Your Powertrain Control Module Be Bad?

Also, keep in mind that on some newer vehicle models, the powertrain control module (PCM) controls charging output. If something goes bad with this circuit, it can prevent the alternator from properly charging the battery. Consult your vehicle repair manual and, if necessary, have the computer's voltage control system checked.

Over time, an undercharged battery will build up lead sulfate around cells and destroy them.

Over time, an undercharged battery will build up lead sulfate around cells and destroy them.

Is Your Battery Sulfated?

A battery that sees little use will eventually become damaged.

You may rarely move your vehicle, store the battery in your garage for long periods at a time, or drive short trips. Any of these conditions will deplete the battery charge.

If the battery discharges almost completely, this will prevent the battery from accepting or holding a charge.

Sometimes, it is possible to bring a sulfated battery to life by slow-charging the battery. Some auto parts stores will trickle-charge your battery for free.

To prevent battery damage, you can buy a trickle charger (battery maintainer) and keep your battery hooked to the charger when not in use. This will keep your battery in shape and prevent possible damage.

VIDEO: What If Your Battery Charger Won't Charge Your Battery?

If your battery has such a low charge that a charger won't work on it, you still may have a chance of restoring your battery's charge. Watch the next video.

Resources on Battery and Charging Problems

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2022 Dan Ferrell