Battery’s Good, But the Car Won’t Start. Now What. 12v car battery voltage

How to use a Multimeter to Test a Car Battery

Here, we check the charge, or voltage, of your car battery. This is achieved by measuring the DC voltage of the battery in parallel with the multimeter. If you are looking to test for amperage draw (parasitic draw) – testing amps in series – we cover that process in this guide.

Other than trying to start the engine to see if there’s charge, the best way to decipher a car battery’s status is to test it using a multimeter. Digital multimeters are the best option for this since they give a more accurate reading, although you could also use an analog one. And even a cheap, category I (CAT-I) multimeter is fine as you are merely testing voltage, not amperage.

If you don’t know how to use a multimeter to test a car battery, read the procedure below:

Step 1: Set Multimeter Ensure the ignition, lights and radio are off.

Select the DC volts position on your multimeter (or the 12V setting if you have a dedicated car battery test range). DC voltage is usually marked as a V followed by a short line with a dotted line beneath it. The wavy line after a V is AC (alternating current) voltage and is for checking the mains voltage in your house.

Most of the manual ranging meters have a 20V range, which is what you would need to test a car battery. The 20V range means it will measure between 0V and 20V. See below:

Step 2: Test Battery With the red lead plugged into the voltage (main) terminal of the multimeter and the black lead plugged into the common (COM) terminal of the multimeter: position the red lead onto the positive (, usually red) terminal of the battery and the black lead to the negative (–, usually black) terminal.

Step 2: Read Meter The meter is now connected in parallel with the car battery and will display a reading automatically. Note the DC volts reading and compare with the table below, which indicates charge, under no-load, status:

Car batteries provide 12.6V DC (direct current) through six cells, producing 2.1V each.

~12.6V: fully charged ~12.4V: 75% charge ~12.2V: 50% ~12V: 25% 11.9V and below: effectively zero charge

Step 4: Check Results Anything under the 75% charge rate, or about 12.45V, generally indicates the battery is undercharged and will need recharging. It does not, however, indicate that it is bad. If after recharging it doesn’t hold the charge, then it is probably on its way out.

Step 5: Recharge Battery If it is under 12.45V, charge it up. You can do this with a portable charger plugged into the mains, which will apply gradual current and take time. The other option is to drive the car for around 30 minutes. Note: it is not enough to just start the engine and let it sit; you want it working under load to receive a proper charge from the alternator. Another option is to get the battery charged at your local auto parts store.

After charging, perform the same test as above to see if the battery now registers in the 12.6V range. If not, consider getting it checked out fully prior to a replacement.

Diagnostic Tests

When fully charged, the battery can be tested further using a couple of methods:

battery, good, start, voltage

Load test: a load is applied to the battery while its voltage is monitored. You can do this by starting the engine and monitoring the voltage with a multimeter that has a Min/Max mode. This will automatically store the high and low voltages it picks up. The high voltage will likely be in the 14V area and is perfectly normal, while a drop under 9.6V during the process would indicate it can no longer effectively hold charge and needs changing.

Electronic test: checks the battery cells via a frequency test.

Some auto parts garages can perform these test for free, either by driving there or taking the battery in. Alternatively, repair shops may also offer a free test, plus the cost of potential repair.

Battery Chargers

There are different types of automotive battery chargers, from basic 2A trickle chargers to more expensive 10A general purpose devices. So-called Smart chargers adjust their voltage output depending on the status of the battery and can charge faster and more efficiently. There is also less chance of overcharging and they can detect whether the batter is 6V or 12V, as well as the type (such as wet or gel cell) and adjust the output accordingly.

CAUTION: car batteries should never be overcharged. Once they reach full charge, it is time to unplug the charger. This is where Smart units are advantageous, preventing damage and thus extra cost. Also, avoid running a known bad battery as you could end up ruining the alternator. They are built to maintain charge as opposed to keeping dead ones alive.

Low Charge and Longevity

Of course, a repeatedly low charge doesn’t mean your battery is dead. It could be good and several scenarios might lead it to lose its charge: such as lights being left on, undriven for long periods, dodgy alternator, or even parasitic draw through any number of electrical circuits in the car going awry. Even an errant radio or internal light connection can repeatedly flatten a good one. But a positive outcome of the tests outlined above should prove the battery itself can hold a charge.

It is worth keeping on top of a battery that continually loses its charge as one that keeps dropping below 75 percent will eventually lead to damage. Most automotive batteries can last four or five years, but one under constant strain from a defective alternator or parasitic draw may fail earlier. On the other hand, if it is four years old and starting to flatten, it may need changing.

Bad Connections

Charge may also be lost in the circuit through bad battery connections. As car batteries are low voltage, the connection needs to be that much better. As is the case with many cars, over time connections are prone to becoming loose, dirty and open to corrosion.

You can check for voltage drop between the battery terminals and cables by first testing on the terminal and then on the wire crimps going out. Anything over around 0.1V less than what is coming out of the terminals suggests high resistance/bad connection. Clean the terminals/connections with sandpaper and tighten them up.

Replacement Car Batteries

When replacing a battery, it doesn’t have to be the same make, but it needs to have the same ratings. The replacement should have the same Cold Cranking Amps (CCA) rating (or higher) as the original. The CCA rating is critical since it is the projected amperage an engine draws when starting in cold weather conditions – i.e. when a car battery will be put under most strain. Put a lower rated CCA battery on an engine that is rated higher CCA and you’re in for problems as it will overload it. CCA is often several hundred maps, and even 1000CCA with larger vehicles.

You should also check the Reserve Capacity rating (RC), which is the time (in minutes) a battery will deliver 25A and maintain 10.5V. You are looking for a higher reserve capacity should the charging system fail.

Better batteries with a higher CCA rating tend to have better warranties attached to them, for obvious reasons. A new battery with a 72-month warranty would be in the premium bracket.

Installation: if installing a replacement yourself, ensure the terminals and the cables are cleaned off and in sound condition.

A Note About Multimeter Types

Some multimeters – usually the cheaper ones – tend to have both the AC and DC voltage ranges sharing the same position on the dial selector. Unless your multimeter is specifically made for the automotive market, it will likely default to AC voltage. Don’t fret as you can easily switch between the two, usually via a ‘select’ switch either below the display or in the center of the dial.

The basic Fluke 101 is an auto ranging multimeter with separate AC and DC voltage ranges:

Most meters today are auto ranging, meaning after setting it to DC voltage, you won’t need to do anything else. The other, older type is a manual ranging multimeter, where you need to select the correct range regards the projected value of the circuit you are going to test. Most of the manual ranging meters have a 20V range, which is what you need to test a car battery. The 20V range means it will measure between 0V and 20V.

Tip: if you are a beginner looking how to use a multimeter to test a car battery to ascertain its voltage, consider getting one that has a dedicated battery tester range on it. The INNOVA 3320 is good for this. Other popular automotive multimeters include the INNOVA 3340 and the top of the line Fluke 88V.

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.


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.

Let’s walk through how long it takes to charge a car battery, how to do it step by step and how to avoid overcharging.

We are so spoiled by our phones and household electronics. We just plug in our phones, Nintendo Switch or electric toothbrushes whenever their batteries get low.

Charging your car battery takes a few more steps because it’s a manual process.

Your car battery isn’t designed like other electronics. Most devices in your life (and their batteries) have electronics programmed with charging instructions. They’ll follow exactly the right steps automatically. For instance, your phone battery has a thin strip of electronics. That’s how it can talk to your phone’s processor. They chat about voltage, amperage rates and float charge times. It’s a lot of computation to lengthen that battery’s lifespan.

Your car battery doesn’t have any of that.

Once your battery starts the engine, the alternator charges it while you drive. Meanwhile, the charging system and the onboard computer regulate the alternator’s output. The alternator does enough to maintain a car battery through a normal battery lifetime of 3-5 years. That’s usually just fine.

However, you may need to charge your car battery

  • if you just jump-started your car.
  • if you notice odd behavior in your accessories.
  • if you left an interior light on overnight (but the car still starts.)
  • if the ignition sounds different to you.
  • if your car had a slow or sluggish start recently.

If that’s you, your car needs help. Regular driving won’t fix it. Your car’s alternator cannot fully recharge your car battery. That’s why you might need to hook it up to a charger.

How to recharge your car battery

Make sure you’re outdoors or in a well-ventilated area. Take off any jewelry, put on gloves and put on safety glasses.

  • Plug in your charger. Consult any specific instructions for your charger.
  • Connect a backup battery to the On-board Diagnostics II (OBD-II) port. Your car’s onboard computers need power all the time. Losing power wipes their memory, and that can cause real car problems, including erratic idling behavior.
  • Disconnect the car’s negative (usually black) terminal. Then put a rag or a glove around the terminal to prevent it from touching anything else. Disconnecting the negative will protect your car’s electronics from the charging voltage.
  • Connect the charger to your car battery terminals. Your charger’s clamps should match the posts. Be careful not to touch your charger’s terminals to the negative terminal you just disconnected.
  • Set the voltage to 12 volts and choose “flooded” or “wet” for the battery type. Flooded and wet are car industry terms for a regular car battery, as opposed to an AGM battery, enhanced flooded battery or a lithium battery. If you’re using a Smart charger, it may detect the voltage and battery type for you.
  • Start the charger and wait. Depending on your battery charger, it may take 4-8 hours to charge your battery enough to start the car a few times. It may take 10-24 hours to charge your battery up to 100 percent. The longer you charge it, the more strength the charger can put in the car battery.
  • Disconnect the charger from the battery when it’s done. Your charger’s indicator light will signal when it’s done charging the battery. Again, avoid letting the charger’s clamps touch the battery’s loose negative clamp.
  • Reconnect the car’s negative terminal to the battery. Disconnect the backup battery. Now you’re ready to hit the road with a fresh start.

Charging your car battery will warm it up. If it gets too hot, the water inside the battery evaporates. In turn, the liquid inside gets more acidic. That means the battery’s insides corrode much faster. The solution is to charge your battery slowly. You want to raise its charge without raising its temperature.

Choose the best battery charger from Interstate Batteries ®

The Interstate Guardian™ 4-amp Smart charger delivers a fast charge and automatically switches to a maintainer to keep your car battery strong when you need it most.

Recharging your battery can add months to its lifespan. It also strengthens the battery so it can better serve your whole engine. The car battery does more than start your engine. It protects your onboard electronics from the engine’s stray power spikes. It also backfills your alternator if your engine or electronics need more power than the alternator can give at any moment.

If you’ve ever noticed your car is more responsive right after getting a fresh battery, that’s why!

Your car really does feel better with a fresh, fully charged battery.

What types of battery charger should you use?

Use an automatic battery charger that adjusts its charging voltage for the fastest charge.

Chargers vary significantly, even within their types. From trickle chargers to Smart chargers and maintainers, the biggest difference between battery chargers comes down to how long do you plan to charge the battery:

  • Use a Smart or automatic charger for 10-24 hours. It depends on how weak the battery is and which amp settings your specific charger uses. Your car battery will be 100 percent charged when it’s done.
  • Use a trickle charger for several days to a week. The most common charger type, trickle chargers, use far fewer amps but can push enough power into the battery to charge it slowly. Some trickle chargers are solar powered. Others plug into a wall. They all provide a steady trickle of power.
  • Use a battery maintainer for months. These don’t charge batteries. If you charge a battery to 75 percent and then hook it up to a maintainer in the fall, it’ll still be 75 percent next spring.

Another device you might find sold beside a battery charger is a jump-starter.

However, jump-starters do not charge your car battery. They only send power (through your car battery) to the starter so you can get going again.

Is your car battery losing charge?

That might be a sign it’s about to fail. Bring your car to any repair shop or Interstate All Battery Center® for a fast, accurate battery test. Each test shows how well a car battery can hold a charge — and whether it’ll fail in the next year or next week.

How a car battery charger works (and why it takes so long)

Charging a battery is like blowing air into a balloon.

At first, you can push a lot of air into the balloon without much effort. Then you have to blow harder as it fills up. When it’s almost full, you’ve got to blow as hard as ever. At that point, you’re working just as hard to keep air in the balloon instead of blowing back into your face.

Car battery chargers go through three phases as they charge a car battery:

  • The bulk phase. The charger raises the battery up to 75 percent in a few hours because it doesn’t have to raise its voltage much to fill it with amps. The charger takes this process slow to keep the battery from getting too warm. By the way, a car battery at 75 percent is not going to reliably start your car for long.
  • The absorption phase. Now the charger must raise its voltage to push the last 25 percent into the battery. As it charges up, the battery’s voltage returns to a normal 12 volts. The charger needs more voltage to finish pushing power into the battery. Higher voltage can heat up the battery, so the charger goes slow. It may take hours to absorb its new power.
  • The float phase. This phase keeps the battery’s voltage up until you’re ready to take it off the charger. Now your battery is up to 100 percent, so the charger turns into a trickle charger. After all, an idle battery slowly loses its charge.

The signs of overcharging a car battery – and how to avoid overcharging

Use your senses of smell, hearing and touch to check your battery for overcharging. Turn off the charger if you sense any of these while charging your car battery

  • The smell of rotten eggs
  • A hissing sound from the battery
  • Heat from the plastic case

These signs mean you are hurting the battery. If you hear a hiss or smell rotten eggs near the battery, that’s a sign that water vapor is escaping. The battery is getting so hot that water is leaving the battery.

To avoid overcharging, check your charger’s settings. Look at your car battery’s label to make sure you’re using the right settings. Most car batteries in the market today are a wet, or flooded, car battery. Using the wrong setting to charge it could hurt your car battery.

Only use the AGM setting if your battery is an absorbed glass-mat battery.

battery, good, start, voltage

Only use the lithium setting if your car battery is a lithium battery.

Only use the 6-volt setting if you’re charging a 6-volt battery. Car batteries are 12 volts.

Check your charger’s instruction manual. That should answer most questions about which charging program works best for your car battery.

Plus, always check on the charging battery. Despite whatever the charger’s box advertises, you should never connect a charger to a battery and walk away. Monitor that it’s working properly first.

Take care of your car by taking charge of the car battery.

Take care of your car by taking charge of the car battery.

You don’t have to be surprised by a dead car battery. Get a battery test at any of our locations. Then you can catch a weak battery—before it fails.

How many volts is a car battery supposed to have?

A fully charged car battery will have 12.88 volts.

Cars run on a 12-volt electrical system. A car battery’s voltage may vary but only in a narrow range, from a fully charged 12.88 volts to a totally dead 11.80 volts.

The difference between a fully charged car battery and a dead one is only 1.04 volts. That slim window means, you should use at least a digital multimeter and not a simple voltmeter with an analog dial.

Use this chart to compare a battery’s voltage to how much charge it has.

You’ll notice that a battery charger can reach higher voltages, up to 13-14 volts. Think of voltage as electrical pressure. A battery charger needs to use a higher voltage to push more power into a mostly charged battery.

However, 16 volts is the limit.

Never let a charger reach 16 volts if you’re charging a battery still hooked up to the car. That much voltage can damage your car’s onboard electronics. Automatic chargers will monitor the voltage. They’ll cut voltage before going past 16 volts to protect the car’s electronics.

If you’re not 100 percent sure how to charge your car battery to 100 percent, we can help.

Visit any Interstate All Battery Center or a repair shop where Interstate is sold. The experts can charge it for you and answer questions about your specific charger and car battery.

How long will it take to charge a car battery?

About 10-24 hours, depending on how weak your battery is. If you’re using a trickle charger, expect it to take days.

Don’t expect an under-charged battery to do the job of a fully charged one. Take your battery off the charger early, and you may risk needing a jump-start later.

Protecting your car battery from heat is why it takes so long to charge it.

Moving electricity around generates heat. Heat hurts your battery. If your battery gets too hot, the water inside will evaporate, leaving too much acid for the internal parts. Of course, all batteries will wear down over time.

However, overheating your battery will shave years off its lifespan.

Charge your battery or get a fresh start?

Check your car battery’s health at any Interstate All Battery Center® store or repair shop where Interstate® is sold. One battery test can prevent a dead battery from stopping your day.

So, charge your battery in a cold place to protect its lifespan. Expect it to take longer than one afternoon. It may take all day to get your battery up to 100 percent.

How long does it take to charge a car battery from driving?

About 4-8 hours at highway speeds. But you can’t charge the battery to 100 percent that way.

Whatever myth you’ve heard, you cannot charge your car battery with 30 minutes of driving. The car’s alternator is not a car battery charger. Yes, your alternator can charge your car battery—if you’re driving on the highway for hours.

Driving for 30 minutes is enough time to warm up your car battery. Maybe the engine will feed it one or two amps.

However, your alternator cannot charge your car battery if you’re going 40 mph for a 10-minute drive and stopping at red lights. The alternator is too busy. It sends power to every electronic device, every light, every engine sensor. If it has amps to spare, yes, the alternator charges the battery a little. The alternator is not a battery charger. Its real job is running the onboard electronics.

So you just jump-started your car. You want to drive it around to charge it. You want to know how long it’ll take and how far you should go.

Better get ready for a road trip.

Let’s say your car battery is just 50 percent charged, which is possibly why you needed a jump-start. It’ll need 8 hours of charging to raise the charge up to 75 percent or 80 percent. Also, if you tap the brake or dip below 1,000 rpm, it stops charging the battery. Going 65 mph would generate enough power to send a worthwhile charge to the battery.

That’s 520 miles. About the distance from San Diego to Sacramento.

Even then, it won’t be fully charged. You could redirect more power to your battery. Turn off the AC, turn off the radio, turn off the headlights, stop charging your phone and use as few electronics as possible. However, you can’t make a big difference that way. Dozens of unseen electronics still need your alternator’s power.

Change or charge your car battery? Test it first.

At any of our locations, you can get a battery test to see how much longer you can trust your car battery.

Whoever told you that driving for 30 minutes will charge your car battery is wrong. That’s like saying you can charge your phone with 5 minutes on a charger. The science doesn’t support the claim.

Take it from the battery experts.

How long does it take to recharge a car battery with jumper cables?

Forever. Don’t do this. Please, do not try to charge a car battery with jumper cables. The current from the running car is passing through the dead car battery, going straight to the dead car’s starter. The good car is pushing enough pressure in to turn the dead car’s starter.

And before you ask, no, revving doesn’t charge the battery substantially.

Revving the good car’s engine will increase the voltage and flow of amperage, but it’s not charging the dead car battery. All you’re doing is spending gas to brighten another car’s dashboard lights.

How bad is it if a car battery goes dead?

Car batteries get permanently damaged if they stay low on charge for a few hours.

If you had to jump-start your car, then your battery was at 40 percent or 50 percent all night long. Those eight hours were long enough to cause serious, irreparable damage to your car battery.

In fact, it may have cut your car battery’s lifespan in half.

It’s because of a process called sulfation.

You see, if you drain a car battery to 30 percent power and leave it there, the battery starts to die.

The science behind it goes like this.

Literally, the parts that held electricity harden. Hardened patches and spots on the lead can’t hold a charge anymore. When that happens, the battery can’t store as much power as it used to.

As a car battery gives power, the sulfuric acid and water inside bonds to the lead plates. The lead turns into lead sulfate while the liquid mixture becomes mostly water. Recharging the battery separates the lead and sulfur molecules.

If you don’t recharge it within hours, that bond hardens in place.

A damaged battery won’t ever recharge to 100 percent again. If the battery was at 50 percent when it sulfated, then it might only charge up to 50 percent and then stop.

Can a totally dead battery get recharged back to full health?

No, you cannot recharge a totally dead battery to 100 percent.

If its charge dropped to zero percent, permanent damage already started. The only question is if you can recharge it soon enough to prevent more damage. If you’re fast, you may recharge it significantly. The right battery charger might even reactivate some deadened internal components.

That said, you might not get it back to 100 percent charge. Even after several days charging it.

Instead of trying to rehab a dead car battery, recycle it.

A permanently damaged car battery is a real drain on your car. It will only hold back your engine. At worst, it could wear down your alternator or leave your electronics short on power if the alternator needs help. Running on too little power can introduce pesky problems that are hard to diagnose. Shop techs know them as gremlins. They can be as mild as Windows that hesitate going up or down or as severe as irregular revving when the transmission shifts gears.

In general, one of the best ways to avoid these gremlins is to give your car a fully charged car battery.

Worried about a dead battery? Come in for a test.

Dead batteries don’t need to surprise you. Visit any place Interstate® is sold for a fast, accurate battery test to see how long you can trust it. We’ll help you replace a weak battery before it fails you.

What Voltage Is Too Low For A 12 Volt Battery? (How to Maximize Battery Life?)

Did you ever wonder what voltage is too low for a 12-volt battery? If so, you need to know this first. Generally, a 12V battery isn’t a 12V battery. 12 Volts is only a convenient and nominal term to differentiate one battery from another.

A fully-charged 12V battery measures around 12.6V between the terminals. So if 12.6V is the standard charge, what figure means it’s too low? Let’s find out.

What Voltage is too Low for a 12 Volt Battery?

When your battery reads only 12V, it’s almost entirely depleted. If the battery’s resting voltage is only 12-12.1, it means only 20-25% of the useful energy is present. The battery is either useless or deep-cycled.

Remember, the battery can only be deep-cycled a certain number of times before it’s considered dead. A standard 12V battery usually has around 12.6V when you fully charge it. So, any reading below that means that it needs to be charged. Anything under 12V means the battery is dead.

If it goes lower than 12V, your battery will get damaged because of too much sulfation.

Checking the Battery Voltage for Better Performance

Remember that the voltage in your battery is kept plays a huge role in determining its service and performance. If your battery is always fully charged, it will last longer than batteries that are undercharged or kept at lower voltages.

To check its voltage, you need to use a voltmeter which you can purchase from most auto parts shops. When you have one, check the battery voltage to determine what you must do next. When your battery is 12.6V or higher, it is healthy and fully charged. That means it’s all good, and no further action is necessary.

If the voltmeter gets 12.5V, your battery is still healthy. However, it’s best to recheck its status within a few days to guarantee that its voltage hasn’t dropped further.

12.4V to 12.1V means your battery is slightly discharged and needs recharging as soon as possible. The lifespan of your battery will get slightly affected if it stays within this range for longer periods.

If it goes below 12.0V, your battery is considered flat or fully discharged and needs to get recharged immediately. The life of your battery will be greatly affected if it stays in this volt range for longer periods.

What Happens When Your Battery’s Voltage Gets too Low?

If the voltage of your battery gets too low, it will get damaged because of too much sulfation. Sulfation is the formation of lead sulfate crystals on the battery’s lead plate surface. On normal cycles, the build-up of crystals is temporary and reverses when you recharge the batteries.

When your batteries get excessively drained, the soft lead sulfate crystallizes. Once that happens, the crystallized lead sulfate will stay on the battery plates and will throw off your battery’s chemical balance.

Once this happens, it will decrease the overall output of the battery and will simultaneously shorten its lifespan. If you allow too much crystallization, your battery will no longer work efficiently. Plus, it won’t provide adequate amperage to start your engine, if it’s a car battery, so you’ll need to replace it immediately.

What Causes Batteries to Drain?

Your driving habits have a huge impact on the lifespan of your battery; however, it isn’t the only factor to consider. Corrosion, extreme weather, and even the technology you have in your vehicle all add to the extra stress on your battery.

battery, good, start, voltage

If your charging system doesn’t work properly, your car battery can drain even when driving.

Remember, many cars power their radio, lights, and other systems via the alternator. This can drain your battery even more, especially if there’s a charging issue.

How to Keep Your Battery Charged

You might be surprised, but the best thing you can do for your car is to make it move – drive it. Your battery uses up tons of energy when you start the car. From there, the alternator replaces the lost or used energy while you drive. The recharging process takes about 30 minutes when you’re going around at highway speeds.

If you’re thinking of driving around the area an additional half-hour each time you start your car, that’s not it. Instead, try to take your car for a 30-minute drive at least once a week. Doing so is essential if you tend to make a lot of quick trips wherein you often start and stop your car.

But if you have to leave your vehicle unused for a matter of weeks, that’s a different story. Your car battery will likely need attention the next time you use and drive your car.

The best thing to do is to ensure that it’s fully charged. If it comes with removable caps, check if it has the right electrolyte levels. You can contact an automotive shop for further assistance when in doubt or aren’t confident.

How to Maximize Your Battery Life?

Most drivers will agree that unexpected flat batteries will give a huge headache. Earlier, we mentioned that different factors, including extreme weather conditions and how you use your vehicle, affect the lifespan of your battery. Luckily, you can prevent the life of your battery from getting flat prematurely.

On average, these batteries can last from three to five years. If you want to avoid changing your batteries in just one or two years, there are ways to do that.

Recharge the Batteries Every Three Months

To maximize the lifespan of your battery, it’s best to recharge your batteries using the correct battery charger. Also, do this every three months to keep its peak performance.

Even if the battery is fully charged, use the right multi-stage battery charger. Doing so will benefit your battery’s overall state, health, and life.

Make Sure that Your Batteries are Kept Clean

Yes, you need to keep these clean too. Remember, dirt, grime, or dampness on your car’s battery can cause leaks across its case, leading to short circuits. In turn, this could lead to a flat battery.

You can easily remove surface-level grime using a sponge and dry cloth. We suggest you do this at least once a month to prevent any build-ups.

Unfortunately, it’s common to have corrosion on battery lead clamps and terminals. When this happens, corrosion can prevent the smooth flow of electricity throughout your battery.

So, build-up and grime must be cleared to guarantee the efficiency and longevity of your battery. When needed, it’s best to ask your mechanic to clean all terminals when you service your car.

It’s good to note that leaving your battery clean is a great way to keep its efficiency and longevity. First, ensure that the top of the battery is clean and that all terminals have no signs of corrosion. Additionally, you can apply a thin coating of high-temperature grease to cable connections and posts for more protection.

Avoid Using Electronic Accessories When the Car Engine isn’t Running

Switching your interior lights/headlights on or your car’s ignition to run infotainment systems without starting its engine isn’t good. Doing this will drain your battery.

Your car’s alternator is shut down when the engine isn’t running. So, using electric accessories during these instances will drain the power from your car’s battery.

You can get into the habit of checking your lights and everything else and making sure they’re switched off. Do this every time you exit and leave your car.

Also, never forget to lock your car when you’re leaving it. Aside from security purposes, your car’s computer system may still be running if you leave it open/unlocked. In turn, this could drain your car’s battery without you knowing about it.

Be Observant and Notice Warning Signs

Your car’s dashboard usually comes with a battery symbol that shows if your battery is down. Familiarize yourself with the other signs that show your battery is draining faster than usual, and these are the following:

  • Your car is starting to make unusual and weird noises
  • The lights on your dashboard are getting dimmer
  • There are clicking sounds when you switch on the ignition key
  • Your car accessories aren’t working how they should

If you notice these signs, you need to get into action. Immediately check your car or have it checked by a professional before your battery worsens.

Make Sure to Get Your Car Serviced Regularly

To prevent unexpected breakdowns, you should have your car’s battery tested and serviced by a professional. So during your next car service, ask your mechanic to check if your car battery is still in good condition. Also, have them check if it’s charging properly.

How to Know if You Need to Replace Your Car’s Battery

Does your car’s battery frequently die, or do you need a few attempts to start your car’s engine every morning? If that’s the case, your battery likely needs replacing. Also, you might be seeing the Check Engine lights, and that’s another sign it needs changing.

If you want to be sure, pop the hood and check the battery. If you see any corrosion build-up on its terminals, that’s another sign that it’s past its prime and needs some changing.

Final Thoughts

The voltage on your 12V battery is too low if it’s reading 12V or below. A standard battery should read around 12.6V when fully charged. If you’re battery struggles to maintain a healthy voltage, then it’s a good sign that it needs to be replaced.


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