How to test car battery and alternator yourself
Updated 10 months 1 week ago
In this article, you will learn how to test a car battery and alternator yourself, at home. Determine if the battery is good or needs to be replaced. We will show you how to perform a load test which tells you if the alternator is providing the required voltage. If your car won't start or doesn't stay running, usually on of the first troubleshooting steps is to check the battery and alternator. Checking the battery is very easy if you have a car battery tester.
What you will need
For this test, you will need a car battery tester. When buying a car battery tester keep the following specs in mind.
- Tests battery on the car directly without removing it
- Check 12 and 24-volt charging system
- Test 6-volt and 12-volt batteries
- Works on AGM, Lead acid flooded batteries and GEL.
- Cold Cranking Amps Range: 200 - 1000 CCA
- Detects bad cells
- Load and alternator test
- Very easy to use
- Works on cars, trucks, vans, boat, SUV.
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How to test a car battery yourself
In this guide, we used Foxwell BT-705 Battery Analyzer which is able to test 6 volt and 12 volts batteries. It can test AGM, GEL or Lead Acid and can test charging systems 12 and 24 volts. It is a great tool if you are looking to quickly and easily perform a load test on car batteries. It also checks charge status and determines if there are any problems with the charging system. This is a great tool even for mechanics. Has a built-in Bluetooth chip that allows you to send reports to any Bluetooth printer. You most likely won't use the print function unless are an auto repair shop.
Step 1: Check battery charge
- Remove key from the ignition. Locate the battery on your car.
- Connect the red clamp to the positive terminal on your car battery.
- Connect the black clamp to the negative terminal of your battery. The battery analyzer should turn on automatically and boot up. If you get an error message saying "Check Connection" make sure the battery posts have no corrosion.
- Hit MENU button and you should see Battery Test option. Press enter.
- Select battery voltage. Most cars use a 12-volt system.
- Select Battery Location. In this case, we select In vehicle. You can also test a battery that is not on the car by selecting "Out of vehicle".
- Present enter and choose post type. In this case, we have Top Post.
- Next, select battery type. Here you can select Regular Flooder (Lead Acid), AGM or GEL battery.
- Enter Cold Cranking Amp CCA which you can look up on top of the battery that you are testing.
- Hit enter to get test results.
Possible test results.
|Good Battery||The battery is in good condition.|
|GOOD-RECHARGE||The battery is in good condition but low current. Fully charge the battery and return it to service. About 75% charge.|
|CHARGE & RETEST||Fully charge the battery and retest. Failure to fully charge the battery before testing may result in inaccurate results. If you still get CHARGE & RETEST message after you fully charge the battery, replace it. Around 50% charge.|
|REPLACE BATTERY||The battery is almost dead or the connection between the battery and battery cable is poor. Replace the battery and retest; or disconnect the battery cables and retest the battery using the out-of-vehicle test before replacing it|
|BAD CELL||The battery may be damaged such as a broken cell or short circuit. Replace the battery and retest.|
How to perform load test / cranking test
- Perform all instructions in Step 1 above.
- When the battery results are displayed press Enter.
- Start the engine.
- Read results of the cranking test.
Possible test results
|Cranking Normal||The starter voltage is normal and the battery is fully charged.|
|Low Voltage||The starter voltage is low and the battery if fully charged.|
|Charge Battery||The starter voltage is low and the battery is discharged. Fully charge the battery and repeat the starter system test|
|Replace Battery||Battery must be replaced before the starting system can be tested.|
|No Start||No vehicle start detected.|
|Cranking Skipped||A start was not detected.|
How to perform charging system / alternator test
- Perform instructions in Step 1 and Step 2.
- Once the results for Cranking Test are displayed press Enter.
- Rev up the engine as instructed.
- Turn on lights and blower fan. If your car has LED lights the tester may not detect that you turned on the lights. Try turning on the high beams or the rear defroster instead.
- Rev engine while leaving the lights, blow, defroster on.
- Determine the status of the charging system.
Possible test results
|No Problems||System is showing normal output from the alternator.|
|No Output||No alternator output detected. Check all connections to and from the alternator, especially the connection to the battery. If the connection is loose or heavily corroded, clean or replaces the cable and retest. If the belts and connections are in good working condition, replace the alternator. (Older vehicles use external voltage regulators, which may require only replacement of the voltage regulator.)|
|Low Output||Alternator not providing sufficient to power the system's electrical loads and charge the battery. Check the belts to ensure the alternator is rotating with the engine running. Replace broken or slipping belts and retest. Check the connections from the alternator to the battery. If the connection is loose or heavily corroded, clean or reparable the cable and retest.|
|High Output||Alternator voltage output exceeds the normal limits. Make sure there are no loose connections and the ground connection is normal. If there are no connection problems, replace the regulator. Most alternators have a built-in regulator that requires replacing the alternator. In older vehicles that use external voltage regulators, you may need to replace only the voltage regulator.|
|Excessive Riple||Excessive AC ripple detected. One or more diodes in the alternator are not functioning or there is stator damage.|
Where to buy this Battery Analyzer
Looking for the best price on a Foxwell BT705 battery tester? Check prices on the following sites.
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A good battery tester should not only be able to measure the voltage but also measure the Cold Cranking Amp (CCA) of the battery. CCA is a better way to determine if the battery is good or not. It also helps you determine the remaining life of the battery. Many cheap battery testers are not able to perform a load test or charging system test. Foxwell battery tester also has printing capabilities which is great if you need to print results at your repair shop. If you are a DIYer you probably won't need to use the printing function. Rember that Foxwell BT705 battery tester can test batteries that are 6 volts and 12 volts and can test charging system that run on 12 volt and 24 volts.
Modern vehicles are sophisticated and very sensitive to battery malfunctions and voltage drops. That's why testing your car battery and charging system is critical, especially if you are experiencing electrical problems or unexplained electrical issues. You can save yourself a trip to the mechanic by using a battery analyzer to determine if the battery is good or not.Back to top