5 Car battery testing methods explained. 12v car battery tester

car battery testing methods explained

Not all shops are willing to invest in such a broad array of tools for battery service and diagnostics, so it’s important to have a good understanding of all the options.

Variations commonly found amongst 12V batteries on the market are absorbed glass-mat (AGM) and flooded lead-acid batteries (serviceable and non-serviceable). While diagnostics are similar, service and maintenance vary based on accessibility and chemical/structural variances amongst each type. Common testing procedures include the use of the following tools: digital multimeter; conductance tester (low amperage tool); refractometer (if battery is serviceable); load tester (high amperage tool); and/or PicoScope 4425A Digital Storage Oscilloscope (battery test option in PicoDiagnostics software).

Not all shops are willing to invest in such a broad array of tools for battery service and diagnostics, so it’s important to have a good understanding of all the options.

Digital multimeter (DMM) testing

While DMM’s do not provide a light-speed reaction to voltage variations based on sample rate, they do provide a stable enough reading to project static voltage, continuous declines in voltage, and charging system voltage output. One major issue to consider is where to make connection with the battery during such readings. In knowing that battery voltage is limited to connectivity between post and terminal, I recommend comparing post-to-post readings of battery voltage to post-to-terminal readings. Note that this process may be impacted by battery design, such as side post batteries.

While slight variances do exist amongst manufacturers to indicate a battery’s 100 percent state-of-charge, I typically project 12.6V is the norm (lead-acid). While cranking, a measurement of at or below 9.6V indicates severe battery degradation or poor maintenance, and further assessment must be conducted, such as charge and re-test following battery manufacturer’s recommendations, cell inspection (if serviceable), etc.

Conductance testing

Conductance testers utilize battery source voltage to measure current and infer resistive values in a complex, yet simple manner. This technology is similar to the use of DMM’s when performing basic testing procedures (voltage, resistance, and current measurements) to mathematically project measurable outcomes. The major benefits of utilizing conductance testers to determine battery conditions are the tool’s cost and size. Conductance testers are traditionally handheld, consume very little space, and are typically less expensive than dedicated carts used to assess battery condition. Conductance tester manufacturers currently equip their tools with exportable data files or immediate printable results to document battery condition at the time of measurement, and often include summaries of battery design, post arrangement (side/top/stud), voltage output, inferred amperage output, and battery condition based on tool analysis. This type of testing allows technicians to easily document their findings and display evidentiary results upon completing the test.

PicoScope 4425A Digital Storage Oscilloscope

As the industry continues to use advanced methods of testing, my personal preference for assessing a battery’s condition is the Pico Diagnostics Battery Test. This test centralizes the most comprehensive data, projects dynamically physical values of voltage and current, and creates a file that can be saved, printed, shared, and displayed for reference and illustration.

Battery’s Good, But the Car Won’t Start. Now What?

When your car won’t start, the first thing to do is check the battery. The vast majority of the time when a vehicle refuses to start up, the cause is a battery with little or no juice. However, sometimes it isn’t that easy. If the battery terminals are clean and properly connected, and a battery tester shows that it’s in good shape, you’ll need to keep troubleshooting to find the problem.

This diagram is a little basic and out of date, but it roughly explains the components of a typical 12-volt charging system:

The battery is a vulnerable component because it can be weakened by age, temperature, and even vibration. But it’s not the only component that needs to be inspected and replaced, and as the years have gone by, it’s become one of the more expensive components in the charging system. There was a time when 75 would buy the best battery on the shelf. These days, you’re looking at 140 to 200.

You don’t want to spend that money unless the battery truly is the problem. We’re not only going to describe how to test these components but the order in which you should be testing, which will uncover typical problem areas and save you from spending more than you have to.

Equipment

You’re going to need a few diagnostic tools, but we’ll keep it to the absolute minimum.

The first thing to consider purchasing is a battery tester with a load tester. This kind of tester not only tests the state of charge at rest but also the health of the battery while it’s subjected to the load of a start cycle.

There are fancier electronic testers, but this old-school analog tester has a couple of advantages:

  • You can usually buy one for less than 40.
  • It doesn’t require batteries to operate. This thing is going to be hanging in your garage — unused — for years. (Something that requires a fresh set of AAs is going to fail when you need it to work most.)

If you don’t want to invest in a battery tester like this, you can always bring the car — or just the battery — to a good auto parts store. Most have a battery tester that can immediately tell you whether or not your battery is the problem.

The other thing to consider is a decent multimeter. You can spend a ton of money on one with features you’ll never use. Find one in the 29 to 45 range with a large digital readout and you should be fine.

This Klein Tools auto-ranging multimeter is about 50 and has all the features you’ll need. It’s available at big box home centers, so you won’t have to find one at a specialty electronics warehouse.

One note: a multimeter can test the voltage of a battery, but it won’t run a one-person start cycle on it the way a battery tester will, so we’d recommend getting both. You can have a second person start the car while you hold a multimeter’s probes against the battery posts, but it’s not as convenient.

The other thing every garage needs is a battery charger. Trickle chargers have gotten smaller, cheaper, and more sophisticated over the years. You can pick up a BlackDecker charger that you simply plug in and not think about for around 30.

Testing in Order

If you want to make this as expensive as possible, just start replacing parts without knowing if they’re the problem.

If you want to get out of this as inexpensively as you can, you need to test a few components to find the root of the problem. We’ve laid these tests out in order of (a) ease, (b) expense, and (c) likelihood of failure.

Test the Battery

Even if it’s new, you need to understand what’s going on with the battery. Attach the tester to the battery. If the needle’s not moving at all, then you’ve got a dead battery. What’s more important is its condition under load.

By pressing the “Load Test” button, you’re simulating a start cycle. The battery should be able to hold 8.5 volts for 15 seconds at 0 degrees Fahrenheit. If it doesn’t, then you know the battery is at least part of the problem.

If it does, then you need to start investigating elsewhere.

Test the Cables

Battery cables go bad all the time. Not only do the connections get crusted up with corrosion, but that corrosion can creep down inside the cables, rendering them all but useless.

A voltage drop test can tell you if your battery cable is the problem. Using the Voltage setting on the multimeter, first, touch the probes to the battery terminals to determine the voltage of the battery. A fully charged battery should have about 12 volts ready to go.

To perform a voltage drop test of the cables and terminals, touch one probe to the battery post, and then the other to the terminal. It should read at or near zero. If it’s reading any lower (the numbers will be represented as negative decimals:.0.07, for example), then you’re losing voltage in your cables.

Watch this video for a more detailed explanation:

Check the Belt

If the battery is discharged and the cable connections are good, you’ll want to fully charge the battery and start looking at the condition of the charging system.

The second cheapest component in the entire charging system next to the cables is the belt, so let’s look at that next. For decades now, cars have used serpentine belts with idler pulleys that maintain tension. If the belt is squeaking or showing signs of slippage, it might not be allowing the alternator to work the way it should. If the belt hasn’t been changed and it looks cracked, it’s time to replace it anyway.

It’s typically a less than 50 replacement, but you also want to replace the idler pulley at the same time. There’s a bearing in it that will go bad at the least convenient moment. At best, this will lead to a dead car. At worst, it could blow your head gasket. This is because this same belt not only spins the alternator, but also the water pump. They’re easy to replace and don’t cost much more than the belt.

Test the Alternator

Typically, if your alternator is no good, it’s going to throw a “CHARGE” light on the dash or show you that you’re not running at 14.3 volts. But, you can’t always count on your dashboard to tell you exactly what’s wrong.

Using your trusty multimeter, you can test exactly how much voltage the alternator is putting out. Simply attach the two probes to the positive and negative terminals of the battery, make sure the probe leads are out of the way of any moving parts in the engine bay, and fire the engine up.

The multimeter should show somewhere between 14.2 and 14.7 volts. If it’s showing less, the battery isn’t being charged as well as it should. This will be especially apparent when you’re running accessories like lights, wipers, rear defroster, and the radio. If it shows MORE than 14.7 volts, the alternator is overcharging the battery and will eventually cook the life out of it.

Test for Parasitic Drain

It’s hard to place this test using our hierarchy of ease, expense, and the likelihood of a problem. If you’ve left a light on, that should be easy and free to fix. If you’ve got a short in a hidden wire because a mouse chewed through it, that could be difficult and expensive to diagnose and fix.

In general, though, less-than-obvious parasitic drains aren’t as common as some of the other issues on our list. However, if your battery is discharging overnight — which you’re determining because you’ve charged the battery, then tested the voltage the next morning as described in step 1 — then you might actually have some kind of a constant drain happening.

To perform this test, remove the negative battery cable from the battery. With the multimeter set to the highest amp scale (read your multimeter’s instructions), touch one of your multimeter’s probes to the cable terminal, and one to the battery post.

The readout on your multimeter shouldn’t be higher than 50ma (milliamps). If it’s more than 50ma, you’ve got something that’s drawing power from the battery.

To determine what’s causing that draw, you’ll need to follow the instructions in the video below. The process involves removing and replacing every single fuse in the car one by one until that voltage draw goes to fewer than 50ma.

Check the Starter

If the cables, belt, battery, and alternator are okay, then (and only then) start looking at the starter. Testing it requires taking it out, meaning that you’re probably going to end up replacing it anyway. So unless you’re pretty ambitious, you’ll probably end up at a mechanic shop. But by this point, you’ll be able to provide your technician with a lot of information about the condition of your charging system. That means you save the mechanic time which he’d otherwise be charging you for. That’s a small win in our book.

We hope this information helps get you back on the road with as much money left in your as possible. And hey, if you decide your current vehicle is more than it’s worth, we know where you can find a new one.

Best Car Battery Testers In 2022

GearHungry Staff posts are a compilation of work by various members of our editorial team. We update old articles regularly to provide you the most current information. You can learn more about our staff here.

A car battery tester is an important piece of equipment to have in your tool kit. It lets you know how much charge is left in your car’s battery and whether it operates at maximum performance. After all, you don’t want that long-waited road trip to end on a flat, don’t you? To take the trouble off your shoulders, we compiled a list of the best car battery testers around. Our picks are ideal for cars, RVs, light trucks, and even motorcycles or ATVs. Check them out.

The Best Car Battery Tester

The FOXWELL BT705 is one of the most versatile vehicle battery testers around. It works with all 12V and 24V batteries with a capacity between 100 and 2,000 CCA, including flooded, gel, deep cycle, AGM flat plate, and AGM spiral.

In other words, it’s an excellent choice for either your car or light truck. What makes it different from its peers is the advanced conductance testing technology consisting of premium-quality copper clips and wire. The material maintains a stable communication throughout the testing process, so you can rest assured it’ll provide reliable results.

A big backlit screen displays all important information about the battery’s health, such as the cranking voltage and cranking time in milliseconds. It can even check the battery’s charging system, from the generator’s voltage output to the charging current status.

Providing you with an accurate reading of the battery health status in less than 3 seconds, this useful diagnostic tool also has an attractive price point. Just what you need for quick battery checks at home or on the go. For more amazing products for your vehicle, check out our guide to the best-selling power inverters for cars.

Ideal for both 12V and 24V batteries

Displays cranking voltage and cranking time

Detects common faults of starting and generator charging systems

Quick result return in about 2.5 seconds

Tests multiple types of batteries and rating systems

battery, testing, methods, explained

Easy and intuitive check of faults

Limited info for troubleshooting

Some plastic components feel cheap

If you’re looking for a simple-to-use, affordable battery load tester, then the Schumacher BT-100 might be it. This unit doesn’t have impressive bells and whistles, but it does what it’s supposed to do with incredible accuracy.

Ideal for motorcycles, cars, and ATVs, it tests 6V and 12V batteries. It’s incredibly easy to operate, thanks to its top-mounted rocker switch. Just clamp the color-coded clips to the battery and turn the device on. While there is no LCD screen, the straightforward, analog scale will quickly tell whether the battery is bad, weak, or okay. Made to withstand tough conditions and years of use, this battery car tester also includes a super grip. Just perfect for no-frills vehicle battery testing. Our guide to the top tire pressure gauges features more must-have devices for your car, so check them out.

Very easy to operate and read

Heavy-duty baked enamel steel case

Insulated carrying handle

Excellent for home car battery diagnosis

Not as accurate as digital testers

No additional diagnostic features

ANCEL BST500 is more than a mere battery tester. This advanced battery diagnostic tool is perhaps the best addition to an amateur or professional toolkit. Whether it’s your car, boat, motorcycle, or battery-powered lawn equipment, this is the load tester you need. It’s perfect for 12V and 24V batteries, checking their load as well as starting and charging systems.

Wide applicability includes testing regular lead-acid as well as flooded batteries, AGM spiral, and flat plate, gel, and deep cycle batteries. Furthermore, the tester covers all battery rating standards and displays accurate results in about 2.5 seconds. As you can expect from a premium product, you’ll also be advised on the battery’s load and charge or replace status. You may also be interested in some of the best car GPS navigation systems so check them out.

Advanced battery tester for 12V and 24V batteries

Fast and accurate readings

Built-in printer for record-keeping

Digital battery tester displays results in under 3 seconds

Lightweight and easy to carry

battery, testing, methods, explained

Backlit display makes it easy to test your vehicle’s battery in all light conditions

The printer tends to jam frequently

Recommended by Scotty Kilmer and extremely easy to use, the TT TOPDON car battery tester is a very intuitive device to add to your amateur arsenal. The greatest strength of this tester is its simplicity. There is no complicated analog display, but an LCD screen that shows easy-to-understand results. Few buttons let you run a test, scroll through the menu, or go back.

It’s compatible with multiple vehicle types, from cars to motorcycles to RVs. Just perfect for 12V lead-acid batteries, whether they’re flooded, gel, AGM spiral or AGM flat plate. Compared to other load battery tester, this model brings an unrivaled user experience. Find more quality products for your car by checking out our guide to the car jump starters.

Well-arranged keypad ensures user-friendly operation

Fast displaying of cranking voltage and cranking time

Lightweight yet sturdy construction

Multiple languages supported

Tends to recommend replacing the battery when it only needs to be charged

It’s not the most durable product around

If you’re tired of spending time and money on expensive routine check-ups, but you’re not exactly a mechanic, the KONNWEI KW600 auto battery tester could be the right one to add to your home garage arsenal. It’s very easy to use and delivers the same accuracy as a professional automotive battery tester. Compatible with 12V batteries, it’s an excellent tool to keep in your car, boat, or RV. It can even test motorcycle and ATV batteries.

This diagnostic tester is not only suitable for a wide range of vehicles; it’s also compatible with all 100-2,000 CCA batteries, from regular flooded to AGM flat plate, AGM spiral, or gel. Results are super-easy to read on the large, backlit display. Among other tests, the KW600 can effectively analyze important data such as voltage, internal resistance, AH capacity, cold cranking amp, and overall charge and health status. For more must-have car gear, check out our guide to the best car battery chargers.

Designed for 12V batteries

Real-time display of battery voltage in a waveform

Capability to print out reports via PC

Charging system ripple test

Works on most 12V automotive batteries, including solar batteries

Multi-function as battery, starter and alternator tester

Doesn’t withstand professional use

There is hardly anything more annoying than waking up to a dead car battery. If you want to make sure your vehicle is always ready to hit the road, you need one of the best car testers in your tool kit. A perfect unit for home users comes from TT TOPDON. The BT100 car battery tester is an inexpensive yet highly reliable automotive battery tester that’s dummy-proof and designed for amateurs. Four buttons, a large display, and unique Smart LED indicators are all you need to check your battery’s status at a glance.

Designed to perform an in-depth diagnosis, this tester can also check the various parts of your car’s charging system, including the rectifier, rectifier diode, and generator. Furthermore, it also analyzes the actual cranking voltage and cranking time. Factory calibrated, fast, and accurate, this car battery tester is undoubtedly an excellent choice for your garage. Any serious car owner will invest in a quality tire repair kit, so be sure to check out our reviews of the best ones on the market.

Aesthetically pleasing design

Unique LED indicators feature

LED indicators provide a quick and comprehensive battery diagnostic result

Ideal for multiple vehicles, including cars, motorcycles, and RVs

Interface available in multiple languages

No description of test purposes

Simple enough to use by car owners but performing enough for professionals, the FOXWELL BT100 packs premium quality in a minimalist device. It’s made for 12V automotive batteries, which means it’s perfect to use for cars, motorcycles, boats, RVs, as well as other vehicles or tools using similar batteries. Convenience is part of the game; the tester is portable, quick to start, and boasts an incredibly easy operation. Calibrated and configured right out of the package, it also cuts off the annoying software or updates installing.

Ideal to use at home or on the go, this tester is also capable of analyzing the battery’s health status and detects faults, apart from telling you the load. Thanks to these features, you’ll know whether it’s worth to recharge the battery or if you’d better replace it. We also like its compact design that fits perfectly into the palm of your hand. Lightweight and super-easy to operate, it brings outstanding value for money. You may also be interested in some of the best de-icers from our list, so check them out.

Streamlined four-key operation

Designed for 12V batteries

Service functions include checking the charging status and detecting faults

Compatible with all 12V automotive batteries

Compact dimensions make it perfect for keeping in your car’s emergency kit

Not as professional-grade as advertised

CARTMAN is renowned for its ultra-affordable tools and gear, and its 12V car battery and alternator tester addresses car owners who’d like to run quick diagnostics without spending an arm and a leg on a professional unit. It won’t deliver utmost accuracy, but it’s reliable in that it will let know whether it’s time to replace or recharge your cell.

Designed with home users in mind, it boasts a ridiculously easy operation. Simply attach the clips to the battery respecting the color-coding and turn on the unit. A convenient LED display indicates the state of the battery. Not only the LEDs have different colors for quick diagnostic at a glance, but a brief description next to each LED sheds further light on the matter. Another highlight is the charge check feature that lets you know when charging is complete. Cheap yet incredibly useful, this tester is perfect for helping you understand when to run a thorough check on your car. If you are also looking for the best car gadgets, be sure to check out our selection of the best ones on the market.

12V battery and alternator checker

The simple LED display of battery status

No display and buttons make it very easy to use

Accurate battery status readings

-sized tester is very easy to carry

Alternator testing is not fully accurate

No advanced testing functions

The OTC 3180 is an uncomplicated battery load tester for both home and professional use. It doesn’t run advanced diagnostics, but it’s perfect for checking the status of the battery of your vehicle. With a convenient, portable size and easy-to-read scales, it simply shows whether it’s time to replace or recharge the battery.

Boasting a simple operation, the unit only requires you to attach the clamps on the battery and turn on the load switch. The measurement takes about 15 seconds, and the results are clearly indicated on the scales. Perfect for automotive batteries and not only, but the tester is also ideal for both 6V and 12V cells. Be sure to also check out our guide to the best car waxes that will help you keep your car looking spotless.

Works on 6V and 12V batteries

Determines state of charge cranking and charging volts

Extra-large display with zero adjust

Tests batteries in just 15 seconds

Compact enough to keep in your garage toolkit or trunk

Heavy-duty copper-plated clamps withstand the test of time

Tester has an overall cheap look

Cables are on the short side

Using a car battery tester doesn’t require you to have a degree in mechanics, but sometimes you might prefer an easier approach. If that’s your case, the INNOVA 3721 might be the best car battery tester for you. It’s much easier to use than a classic tester, right from the comfort of your car. Simply plug it into the vehicle’s cigarette lighter or power receptacle and wait for a few seconds.

Results are both displayed on the backlit LCD and indicated by color-coded LEDs. Designed to provide a wealth of information on your battery’s status, the display shows the measured voltage as well as a bar graph that indicates the charge level. The colored LEDs, on the other hand, indicate the charge status, helping you evaluate the efficiency of your alternator. This.sized device also boasts a pivoting head that allows you to make quick viewing and angle adjustments. Perfect for keeping in your car; this is a handy tool can help you run quick battery diagnostics and it makes an ideal gift for car lovers.

Designed for 12V negative ground systems

Plugs into a cigarette lighter

Color-coded LEDs help you identify the battery status easily

Easier to use than most car battery testers

Allows you to check the status of the battery from the comfort of your car

Less durable than expected

Moving forward with our list, the AUTDER digital battery tester is another inexpensive unit ideal for home use. Dubbed “the battery mate,” the tester is designed for 12V batteries. Not as fancy as other digital units but reliable, it shows you the voltage on a small screen as well as the battery and alternator status with the help of LED indicators.

Controlled by a high-quality microprocessor, it provides extra-quick readings. In this way, you’ll know if you need to jump-start or fully replace the battery. Its greatest highlight is the pure copper wire and clamps that deliver outstanding conductivity as well as high sensitivity. This tester doesn’t have many bells and whistles, but it does what it’s supposed to do. A great investment at a fraction of the price of more performing car battery testers. Be sure to also check out our guide to the best car vacuum cleaners for more useful products for your vehicle.

Designed for 12V batteries

8-LED battery status indicators

Four-character digital display

Pure copper clamps and wire

LED indicators let you check the battery status at a glance

Voltage is displayed on the four-digit digital display

Can only run limited tests

Runleader Batery Fuel Gauge Indicator is not a car battery tester in the true meaning of the word, but it does check the health and load status of batteries. Instead of automotive, though, we’re talking about 48V batteries usually used on golf carts, club cars, forklifts, and floor care equipment.

Now, considering all the above are vehicles too – and that some of you might play golf – it’s easy to understand why this tester has made it to our list. than a tester, this fuel gauge indicator does exactly this. It tells you how much of a charge is left in your cell, and whether it’s time to recharge it. Different colors for different load levels make it easy to draw a conclusion. Furthermore, a 10-segment LED bar graph also offers a visual representation of the charge level. Its only downside is that it is quite difficult to install. Our guide to the best rooftop cargo boxes features some amazing products ideal your road trips, so check them out.

Designed for 48V batteries

Unique snap-in installation

Historical data stored automatically

Ideal for a wide range of utility vehicles

LED flash for low charge and high charge warnings

Memory option allows recalling the last reading

Rather limited functionality

Concluding our round-up, the LEICESTERCN automotive battery tester is perfectly compatible with 6V, 12V, and 24V lead-acid batteries. Whether it’s regular flooded, gel, AGM, or deep cycle, this tester has got you covered. Three sets of adapter cables let you choose the preferred connection method. Pick from either traditional clamps or cigarette lighter plug the one that best suits your needs and skill level.

Easy to use even by beginners, the tester also boasts a large LCD screen that displays all essential information. Ultra-compact and ultra-safe thanks to its reverse polarity and over-voltage protection, this tester is one of the best for most car owners, just like some of the best timing lights from our list.

Suitable for 6V, 12V, and 24V lead-acid batteries

A quick evaluation of your battery’s condition

Very safe and accurate to use even by rookies

Ultra-compact design, perfect for keeping in the car

Comes with three adapter cable sets

Overpriced for what it offers

It uses power from the battery it testes

Features To Look For In Car Battery Testers

The market is full of car battery testers, but if you want to get the best battery tester, you should pay attention to the following features.

Type – We can distinguish between two types of battery testers, analog and digital. The former is the simplest model that simply show you the test results on a scale. Digital units usually display more information, including voltage, on a digital LCD screen.

Functionality – Some car battery testers will only let you know the charge status of the battery, and maybe if the battery’s faulty. Other testers can also check your alternator and display more information about the battery status. Which one is the best is down to you, based on your knowledge, needs, and skills.

Battery compatibility – When buying a car battery tester, remember that not all vehicles were created equal. Most testers around are compatible with 12V batteries used on most cars, light trucks, and RVs. However, we recommend checking the type of battery your vehicle uses before investing in a tester.

Cable length – Last but not least, also check the cable length. Some testers have short cables that require you to stay outside, near the battery. Others have longer cables that allow you to get a reading from the comfort of your car. Alternatively, some units plug into the car’s cigarette lighter to test the battery. Before buying, consider your needs so that you can pick the best car battery tester for you.

How To Test Your Car Battery Voltage ( 9 FAQs)

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Knowing your battery voltage helps you determine how long it’s going to last.

In this article, we’ll answer that question and show you how to test your car battery voltage (with and without a tester). We’ll also tell you how to check your alternator and offer a quick solution to battery testing issues.

We’ll also cover some FAQs to give you a better understanding of car battery voltage and testing.

What Should My Car Battery Voltage Be?

The resting voltage (when the engine is off) measures around 12.6 volts. Car batteries typically provide these 12.6 volts through six cells, each supplying around 2.1V.

When the engine is running, the batterys voltage should fall between 13.7-14.7V.

But what does the voltage tell you?

Measuring the resting voltage can indicate the battery’s state of charge — or how much battery charge capacity remains. In general, for a car battery with 12 volts, the state of charge is:

  • 75% at 12.4V
  • 50% at 12.2V
  • 25% at 12.0V
  • Considered fully discharged at 11.9 minimum voltage.

Note: If you’re curious as to whether 8 x 1.5V AA batteries are the same as the 12 volts in a car battery, the answer is no. AA batteries have too much internal resistance to kick-start a car.

Next, let’s look at a simple battery test for voltage measurements.

How To Measure Car Battery Voltage

To check your car’s battery condition, you’ll need a battery tester, like a simple voltmeter or multimeter.

For measuring the battery voltage and load, the multimeter has two probes: red and black. The red probe is for contact on the positive terminal, and the black probe is for the negative terminal.

Follow these six simple steps to measure the battery voltage:

Safety Measures

Before you begin your battery test, here are a couple of pointers for safety and accuracy:

  • Check theterminalsfor corrosion, as it can increase internal resistance and decrease the voltage reading (check out our guide to cleaning corrosion here).
  • Check thebatteryforleakage, bloating, or damage — don’t work on the battery if the terminals are damaged. An AGM battery will ensure that no leakage can occur.
  • Don’t smoke around batteries, as sparks can trigger an explosion.
  • Wear safety glasses and gloves to protect yourself from battery acid in case of any mishaps.

Note: For a more accurate reading, it’s best to do a battery test 12 hours after turning off your vehicle. This allows any surface charge to dissipate. Otherwise, your readings could be higher than they should be.

Once that’s done, here’s what you need to do:

Turn Off The Ignition

Make sure your vehicle’s ignition is off.

To help remove the surface charge, you can turn on the headlights for 2 minutes. Ensure the headlights are switched off before you test the battery capacity.

Set Up The Tester To Measure DC

Set your voltmeter or multimeter setting to test DC or DC voltage (Direct Current Voltage). If there’s a DC voltage range, set the maximum to read around 20-25V.

Touch The Probes To Each Battery Terminal

Locate the positive terminal and the negative terminal (-) on the battery.

Sometimes the battery post is covered with a plastic cap. You’ll have to uncover the terminal to test, but you won’t have to remove the battery cables.

Your battery tester will likely have a red and black (-) probe:

  • First, touch the red probe to the positive battery terminal
  • Then, touch the black probe (-) to the negative battery terminal

Note: If you get a negative reading, it means your probes are swapped, and you just need to switch the battery post they’re touching.

Check Voltage With Engine Off

A good battery should have a resting voltage between 12.4-12.9V.

If the reading is less than 12.4V, it doesn’t necessarily mean you have a bad lead acid battery, just low voltage. Some electrical system might have drained it, or your alternator has trouble charging.

If the battery voltage is below 12.2V, it needs to be recharged. Try driving your vehicle for at least 15 minutes to bring the low voltage back up. Alternatively, you can buy car battery chargers to charge the battery back to its minimum voltage.

After recharging the low voltage battery, test it again to see if it holds the charge.

If the batterys voltage is over 12.9V, then your car battery has excessive voltage. Turn on your high beam to drain it. This could mean your alternator had overcharging issues.

Note: An AGM battery may display a higher voltage. Check the manufacturer datasheet for details.

Do A Crank Cycle Test

The crank cycle test shows how well the battery performs when delivering voltage to the starter motor.

Get a friend (or use a remote starter if you have one) to start the car.

There’ll be a quick voltage drop as the engine is cranking, and then it will rise again. The voltage drop shouldn’t go under 9.6V. If it does, it means the battery doesn’t have enough turnover strength, and you’ll likely need a new battery.

Measure Voltage With Engine On

With the engine on, your vehicle will idle, maintaining a steady draw from the battery.

The alternator will now charge the car battery.

You can expect to see the battery voltage measure around 13.7-14.7V. If the voltage reading is significantly lower or higher, it could mean issues with the battery or alternator.

But what if you don’t have a volt meter? Can you still check your battery condition?

How To The Check Car Battery Without A Tester

While you can’t accurately measure voltage without a tester, you can still gauge the car’s battery condition.

  • With the engine off, turn on the headlights — they will be your test indicator
  • Get a friend to start the car (or use a remote starter)
  • Watch the headlights as the engine cranks

If the headlights dim during cranking, there might not be enough battery charge.

If the headlights remain steady, but the engine won’t start, then there’s no battery issue, but possibly a problem with the starter motor.

What about the alternator?Is there a way to check it too?

How To Check The Alternator

The alternator is part of your vehicle’s charging system. Here’s how to check if it’s working fine:

A. With A Tester

With the engine running, turn on all the vehicle’s electronics — headlights, interior lamps, stereo, etc. — to maximize the voltage load.

Now, measure the battery voltage.

If the charging voltage drop is under 13.5V, it means the alternator has trouble charging the car battery, and you should get a mechanic to look at it.

B. Without A Tester

If you don’t have a tester handy, you can still test the alternator. Make sure the car is “Park” and the parking brake is on before you begin.

Start the engine without the headlights, then turn on the headlights:

  • If the headlights are dimmer than usual, there might not be enough charging voltage from the alternator, so the headlights are running off sole battery power.
  • If the headlights brighten, the alternator is charging the car battery but not providing enough voltage at idle.
  • If the headlights remain the same, then there’s probably no alternator issue.

Turn on the interior lights:

  • If they dim gradually with a running engine, there could be an alternator problem. Get a mechanic to verify the issue.

Now let’s go over some FAQs about car battery voltage.

Car Battery Voltage FAQs

Here are answers to some common car battery questions.

What’s A Voltmeter?

The voltmeter (or volt meter) is a simple instrument for measuring the electrical potential difference between two points in an electric circuit. Electric potential difference refers to the electromotive force of the battery.

What’s A Multimeter?

The multimeter measures multiple electrical properties — typically voltage (Volt), resistance (Ohms), and current (Amps). It’s sometimes called a Volt Ohm Milliammeter (VOM).

It is used to test if your battery has low or excessive voltage.

You can use a digital multimeter or an analog multimeter.

What’s The Alternator?

The alternator converts mechanical energy from the engine into electrical current for the car battery. It’s the primary element in your vehicle’s charging system.

Generally, the alternator produces more current at higher speeds which means that driving faster will produce more current.

There’s a cap, of course, on how much current the alternator can generate.

How Often Should I Test Battery Voltage?

You should check your battery voltage at least twice annually. This will give you an idea of its condition, so you’ll know when to bring it for further testing or if you need a battery replacement.

When Should I Use A Car Battery Charger?

Hook your battery to car battery chargers if the voltmeter reading dips under 12.4V.

If the reading is below 12.2V, you should consider using a trickle charger which charges at a much slower rate. Using a trickle charger helps avoid the risk of battery overheating and overcharging.

What’s A Car Battery Load Test?

The battery load test is used to test the 12 volt battery under load and is a more accurate battery health indicator than voltage measurement.

A load tester is specifically designed to determine the voltage generated while a load is placed on the fully charged battery.

During this test, the fully charged battery should be loaded with one-half of its cold cranking amp (CCA) rating at 70°F (or more.) A cold cranking amp refers to the battery’s ability to start in cold temperatures.

A good battery will be able to maintain 9.6V for 15 seconds with this load. If the load tester dips below 9.6V during the load test, it might be time for a battery replacement.

How Do I Know If I Have A Bad Battery?

A bad battery can display several symptoms.

Here are some common ones:

  • Engine cranking is slow: this means the battery has difficulty delivering a charge
  • A misshapenbattery: it’s bloated, cracked, or leaking
  • There’s an odd smell: this can come from leaking battery acid in a lead acid battery
  • It’s anoldbattery: the average battery life is around 3-5 years

If you notice any of these, it’s time to get a new battery.

Why Does A Car Battery Drain Out?

Here are some reasons why you might have a dead battery after your engine is off:

  • The headlights were left on
  • An electrical system (like a cell phone left charging) may be drawing amps
  • The battery isn’t being recharged while you’re driving
  • The battery is too old and won’t hold a charge anymore

How Can I Maximize My Battery Life?

Here are a few methods you can use to increase battery capacity:

  • Keep thebatteryclean: Corrosion buildup can drastically decrease the life of a lead acid battery.
  • Check electrolyte level: Remove the vent plugs and ensure that the electrolyte level covers the lead battery plates in all six cells.
  • Recharge yourbatteryevery three months: Recharging with the appropriate car battery charger can maintain peak battery performance for longer periods of time.

What Is An Easy Solution To Car Battery Maintenance?

If you need more than a car battery voltage test, a professional mechanic is your best option. They can handle all the car battery maintenance tasks — including load testing, checking battery cables, and weak battery replacement.

It’s even better if they’re a mobile mechanic and can come to you.

RepairSmith is a convenient mobile vehicle maintenance and repair solution.

Here’s why we’re a great option:

  • Car battery maintenance and fixes can be made right in your driveway
  • Expert technicians execute inspection and servicing
  • Online booking is convenient, and service hours are flexible
  • Competitive, upfront pricing
  • All maintenance and fixes are conducted with high-quality tools and replacement parts
  • RepairSmith offers a 12-month | 12,000-mile warranty for all repairs

Fill out this online form for an accurate cost estimate for your weak, damaged, or dead battery repairs and maintenance.

Closing Thoughts

Batteries lose their ability to hold a charge as they age and eventually won’t be able to charge up to 100%. Measuring your car battery voltage is an easy way to check your battery’s condition to give you a heads-up if you have a weak battery.

And if your low voltage battery needs some detailed maintenance work, you can always rely on RepairSmith.

Contact us during service hours, and our expert technicians will be at your driveway in no time, ready to solve any issues!

RepairSmith RepairSmith is the easiest way to repair your car. Our ASE-certified technicians deliver quality car repair and maintenance directly to your driveway. We offer upfront pricing, online booking, and a 12-month, 12,000-mile warranty.

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