How to check if battery is good

Using a multimeter to test a battery is easy. The first thing to do is make sure you can access the battery terminals (the metal connections on the top or front of the battery).

Table of Contents Show

How to check a car battery with a multimeter
How to check your alternator with a multimeter
How to find dead cells in a car battery
How to Test a Car Battery at Home (with No Equipment)
1. Perform a load test.
2. Check for corrosion.
3. Listen for clicks.
4. Use the virtual battery tester.
Visit Firestone Complete Auto Care.

Batteries are commonly located in the engine bay to one side of the engine. If the battery is not immediately obvious when you open the hood, consult the owner's manual. In modern cars, the battery will often have a plastic cover which will unclip, hinge up, or occasionally require removing with a few bolts or screws. There may also be a red cover over the positive (+) terminal that will lift off or snap open, too.

Once the battery is exposed, be extremely careful that nothing metal touches the terminals and causes a short, so don't rest wrenches or other tools on top of the battery.

Jump starting a battery: the right and wrong ways to do it

How to check a car battery with a multimeter

The first test with your multimeter will measure DC voltage, indicated with a solid line and a dashed line above a letter V. Set the dial to 20, which will allow you to accurately measure between 0-20 Volts.

Touch the red probe to the positive (usually red) terminal, and the black probe to the negative (black) terminal. The terminals will be marked + and -. If you get a reading with a minus in front of it (-12.6 rather than 12.6) you've got the probes the wrong way round!

The resting voltage should ideally be no lower than 12.6V. A battery that reads 12.2V is actually only 50% charged, and is classed as discharged below 12V.

One thing to bear in mind is that all modern cars experience 'parasitic loss', which is when something electrical drains the battery even with the engine turned off. So, systems such as the clock, computer and alarm use some power. If you suspect this is killing your battery during storage, you might be wise to disconnect the battery or remove it entirely.

If the multimeter reads less than 12.6 volts, disconnect the battery and fully charge it using a battery charger. Then let it rest overnight. If it holds a charge when it's not connected to the car – something is draining the battery far faster than the computer memory and digital clock.

Time to change the battery? Here's how to do it

How to check your alternator with a multimeter

An alternator produces electricity and charges the battery. Not only that, but while you're driving it also takes over and delivers power to the car's electrical systems.

So with the engine running (and being mindful about moving parts) conduct the same battery test as above with your multimeter. A healthy charging system should give a reading of between 13.8V and 14.4V at regular idle speed.

Anywhere outside that range and your car's either under, or over charging – both of which will shorten the battery life and require further investigation. For more on the charging system in your car, see When Good Alternators Go Bad (and Why).

How to find dead cells in a car battery

First things first, knowing a battery cell is dead is of no more use to you than knowing that the battery won't hold a 12.6 volt charge, because you can't fix it. So, a test of the resting voltage is just as effective a diagnosis.

A battery usually won't go bad all at once; instead, some of the cells that make up the battery will go dead. An engine that's slow to turn over when starting is often a sign of dead battery cells.

Most new car batteries are of the sealed 'maintenance free' variety, but some older batteries allow you to access the individual cells. The cells will either have individual caps, or a plastic cover that clips over all, or several of the cells. The cells contain a mix of water and sulfuric acid, so make sure you don't get any liquid on your skin.

To test each cell, you need a hydrometer-style battery tester that measures the specific gravity of the battery acid. Based on the number of balls floating, you can tell whether the cell is dead or not.

Pro Tip: Before you disconnect your battery make sure you know the anti-theft code for your stereo – you may find it won't work when you reconnect it otherwise!

Batteries

How to Test a Car Battery at Home (with No Equipment)

Oct 23,2018

When it comes to starting your car, silence is one of the worst sounds you can hear.

That’s why it’s essential to act immediately if you:

Suspect your car battery is losing power (pay attention to warning signs).

You can’t recall the last time you replaced your car battery.

You won’t even have to leave your driveway to conduct a quick battery check. We’ll show you how to test a car battery from home in four simple steps.

1. Perform a load test.

Performing any "test" on your car can sound intimidating if you’re not a technician. Luckily, this one is pretty straightforward.

Without starting your engine, turn on your headlights.

Leave them in the "ON" position for 10-15 minutes.

After that time passes, start your car.

Watch the brightness of your headlights.

If your headlights dim noticeably as the engine turns over, your battery doesn’t pass the load test. The battery should hold enough charge to handle the 10-15 minutes before the engine starts, and once the engine turns over. If your car’s battery is struggling here, it most likely needs to be replaced before it fails you on the road.

2. Check for corrosion.

Besides looking like something that would ooze out of an evil scientist’s laboratory, corrosion on your car’s battery could indicate a power problem.

Over time, that corrosion, caused when acid within the battery releases hydrogen gas, might interfere with the battery terminals’ ability to transfer power. The battery has to work harder to compensate, and that extra work can shorten its life.

You can clean the battery terminals (carefully!) with household items like baking soda and an old toothbrush. If your battery has been suffering from corrosion for a long time, however, the damage may be irreversible. In that case, it’s time to replace.

3. Listen for clicks.

If anyone ever makes a horror movie about car problems, you can bet the soundtrack would be the rapid clicking of a lifeless battery!

When you turn your key over in the ignition, you should hear a lively roar that settles into a purr. When you hear “click-click-click” instead, you know your car battery is likely dead. A single click, on the other hand, could mean a bad starter.

Those clicks might not mean your battery needs to be replaced, but they're a reliable indicator. Even if a jump start gets the vehicle going, the first stop should be the bay of an experienced, trusted technician.

4. Use the virtual battery tester.

The internet’s awesomeness is beyond dispute at this point. One reason? It has everything—and keeps getting cool, new stuff!

One example: you can now “test” your battery online with a virtual battery tester on Firestone Complete Auto Care’s website.

Visit our virtual battery tester.

Enter your car’s year, make, model, engine type, and your zip code.

Click the red “Find Out Now” button.

The virtual battery tester tells you the battery’s expected lifespan. Keep in mind that factors such as corrosion or weather can alter your battery’s life expectancy and influence the test’s accuracy.

Visit Firestone Complete Auto Care.

The best time to replace your battery? Before you need to! If you've done this quick check and you're still unsure about your battery, visit Firestone Complete Auto Care to get a more precise (and 100% free) battery test. We can predict potential battery failures within a minute or less.

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