Can You Recharge A Completely Dead Car Battery?

Having a weak battery when you’re in a hurry is frustrating, and worse, it might leave you stranded. While there are many reasons as to why your battery might keep dying without notice, there are a few things you can do to get the juice back into your vehicle, depending on how “dead” your battery is. 

It is one of the basic car maintenance skills to know when a dead battery is indeed the culprit for starting problems, how to check whether your battery is dead and how dead it is, and whether you can recharge a completely dead car battery. In this article, you will learn the signs of a dead battery, and how to revive it, as well as understand what happens inside a battery when it is dead, when a battery cannot be revived anymore, and tips on how to avoid completely depleting your precious battery. 

When Is A Battery “Dead”? 

“A dead battery” might be a confusing description. Usually it refers to a battery that’s depleted or discharged to such a low level that it won’t supply enough power to effectively start the engine, so you’ll have difficulty starting your car, or your car might not even start at all. 

However, there are different “levels” of battery “death”. A battery might be dead, but just almost, that is when it’s depleted or discharged to a dangerous level but can be recharged again. A battery can die like this and get revived a certain number of times during its life, but after a certain point, it will truly die and cannot be revived anymore. The only option then is to replace your battery. 

It’s important to know just how dead your car’s battery is before you decide how to recharge it. For this, you will need a multimeter or a voltmeter, both are cheap and handy devices for diagnosing battery issues. A healthy battery will show 12.4 to 12.7 volts across both terminals 

If the voltmeter reads lower than 12.4 volts, you’ll likely run into problems when trying to start your vehicle. How much lower will determine what method you should use to charge the battery after jump-starting your vehicle, and below a certain point, your battery will be truly “dead”, that is it cannot be revived in any way and must be replaced. 

Signs of a Dead Car Battery

If you’re experiencing one or more of the following symptoms, a dead battery is very likely the culprit. Some of these telltale signs can also be caused by other underlying issues elsewhere, so it’s important that you test your battery’s voltage with the appropriate tool after encountering these problems to check its condition.

Engine Doesn’t Start 

Your car relies on your battery to get the engine started and running. So when your car battery dies, the most obvious sign is that the engine won’t start when you turn the ignition key. That said, there are many possible reasons for a hard starting problem. To narrow down the culprit, you’ll need to listen carefully when you turn the key. 

If you hear and feel nothing at all when turning the key, it means that the starter motor isn’t getting any power. The starter motor is responsible for turning the engine over when you turn the ignition on to initiate the engine’s operation under its own power.

When in addition to this symptom, you’re also experiencing one or more problems below, then it’s most likely that you’re dealing with a dead, or depleted battery. Otherwise, there are alternate underlying causes, including faulty ignition switch or fusible link.

Engine Doesn’t Start But Starter Motor Cranks

Another possibility is when you turn the ignition key, the engine doesn’t start but you can hear the starter motor. The starter motor always makes a distinct sound when it is engaging with the engine via a toothed flexplate or flywheel and physically rotating it. You should be pretty familiar with the sound your car makes when you turn the key. 

If one day it sounds different or if you don’t hear it at all (as in the symptom above), there is a problem with the starter itself or the battery or other parts. How the sound changes can help you narrow down the culprit.

If the starter cranks at a normal speed, then you have a fuel issue or or faulty spark. If the starter motor cranks a few times and then stops altogether, or cranks very slowly and sounds labored, you’re dealing with either a dead battery or a faulty starter motor. 

The most common cause for this is that the battery does not have enough charge or voltage to properly operate the starter. Thus, the starter motor may be able to turn the engine over, but does not provide enough power so that the engine can start up and run on its own. In some cases, a faulty starter motor might be attempting to draw more amperage or current than the battery is able to provide.

To pinpoint the culprit, you must perform a battery test using a multimeter or a voltmeter to check if the battery has enough voltage, and if all battery terminals are tightly fit and clean (free of corrosion). If the battery is intact and is not dead, then you may suspect a faulty starter motor. You need to use an ammeter to verify that a faulty starter motor is indeed drawing too much amperage from the battery before proceeding to replace the starter. 

Car Needs A Jump In The Morning

Recharge A Completely Dead Car Battery
How to revive a dead battery depends on how dead it is. Photo credit: Revolution-Motors-Edmonton

If you can’t start your car one morning without a jump start, but have no problems later in the day, two things might have happened and the battery is actually not the underlying cause but only related. Firstly, there is a parasitic draw on the battery overnight that has been draining it of its juice. In this case, your battery can be revived or it can die off completely and needs to be replaced. Either way, you need to locate the source of the parasitic drain and try to avoid it.

There are a number of electrical accessories in your car, including the stereo, interior lights, door lights, the dashboard and more. Most of these features typically don’t drain your car battery when the engine is off, but little electrical mishaps can still happen and squeeze your battery of its charge overnight. Interior lights (including door lights) and bad fuses are the most problematic sources of possible parasitic drain. To avoid such electrical mishaps, you should make it a habit to turn off all lights and make sure all doors are fully closed and latched before leaving the car, including your trunk and glove box.

The second underlying cause is extreme cold weather. It’s pretty common to experience a hard start or a no start problem on particularly cold mornings. Severe cold weather can freeze a battery, short out the plates and the battery will no longer charge, or diminish the battery’s ability to provide on-demand current to the starter motor. Lead acid batteries and Lithium Ion batteries are particularly weak to extreme cold weather. 

While younger batteries under 3 years old have higher resistance to extreme cold, a battery loses its strength with old age. So if you live somewhere that frequently gets below freezing point in the winter and find your battery dead one morning, you’ll most likely need to replace it pretty soon, although you might be able to get a few more rides out of it following one of the methods that we’ll discuss later. And you’ll want to get a new battery with a higher cold cranking amps rating to better withstand extreme cold weather.

Some Electrical Accessories/Features Don’t Work

If one day you notice that many electrical accessories or features don’t work properly or at all at the same time, it’s usually a red flag that the battery’s dead and cannot provide power to operate these accessories. 

For instance, the dash lights and headlights might be dimmer than usual or don’t turn on at all, or if you insert your keys while the door is still open but don’t hear the familiar chime, or your dome light doesn’t come on. 

Do note that if something doesn’t work but others still do, then the battery probably isn’t dead. For instance, if your door chime doesn’t work, but other electrical accessories like dash lights, headlights and radio do, the culprit is most likely a faulty door switch or fuse. Or if it’s only the headlights and radio that won’t turn on, the issue can be a blown main fuse or wiring issues.

What Really Happens Chemically In A Dead Battery

As noted above, whether a depleted battery can be recharged or revived by some other methods depends on how “dead” it is. This will decide the best proper way to revive the problematic battery, or whether the battery is really dead and gone and thus must be replaced.

Mistreating a depleted and deteriorating battery will only send it to the end of its lifespan much faster and can also put excessive stress on or damage other components in your car. Therefore, before we move on to discussing the safe and proper ways to recharge or revive a completely dead battery in the next section, you must first grasp what happens chemically inside a dead battery.

A car battery is constructed of alternating plates made from lead (Pb) and lead oxide (PbO2), and these plates are suspended in an electrolyte solution of water and sulfuric acid (H2SO4). As the battery discharges, the battery acid solution facilitates the flow of electrons from the lead plate to the lead oxide plate. This generates an electric current, which is used to power the engine or operate other electrical accessories. 

Because of this chemical reaction, sulfur is drawn out of the battery acid and the lead plates of the discharged battery now become coated in lead sulfate (PbSO4). This process of “sulfation” occurs practically every time you discharge the battery and it is where the potential problem lies.​

If the battery is immediately recharged after being discharged, which is what typically happens, then the opposite chemical reaction will immediately take place and reverse the previous sulfation process. 

When the engine is running, the alternator will charge the battery, or when you connect the battery to a dedicated battery charger, most of the lead sulfate coating on the lead plates return to the battery acid. At the same time, hydrogen is also released. This is why it’s possible to charge and discharge a lead-acid battery over and over again. 

So if the battery stays charged, the sulfation process is reversible, so called “soft” sulfation. However, “hard” sulfation can occur if the car battery is left discharged for an extended period, which refers to the formation of lead sulfate crystals on the battery plates. These crystals gradually reduce the surface area on the plates available for chemical reaction, thus diminishing the battery’s ability to charge and discharge. 

Over time, this will get worse and result in cracks and short circuits within the battery, and the battery will need to be retired for good.

In other words, while the sulfation process occurring on the battery plates is reversible, all types of battery can only withstand a limited number of charges and discharge cycles. Also, every time a battery is completely depleted, it suffers irreversible damage. So a battery can only completely “die” and get recharged again for a limited number of times before it dies for real and needs to be replaced.  

So it means that while in many cases as discussed above, the underlying cause of a hard starting problem is not a dead battery itself and thus you just need to fix it and fully charge your battery to bring the battery to life again, a battery that has been jump-started or charged from dead for a certain number of times will have to be replaced anyway.​

Can A Completely Dead Battery Be Recharged?

Unfortunately, it is impossible to reverse hard sulfation. Still, if you have a dead car battery, there are several things that you can try to get yourself back on the road. That said, what you can do depends on how dead the battery really is. 

If The Battery Is Almost Depleted

Driving Around: As said, a healthy battery should have at least 12.4 volts of charge. In general, if the battery still has barely enough charge in it, that is if a multimeter test is returning a reading between 12 volts and 12.4 volts, it’s safe to recharge it with your vehicle’s alternator. That means you only need to take your car around for a drive to allow the alternator to charge the battery, but you need to use as little electricity as possible to make sure nothing is unnecessarily draining power, and the alternator is sending as much energy into the battery as possible. It’s best to go for a drive when it’s bright outside, and turn off all lights and other electrical systems and accessories. The general consensus is you have to drive the car at least 30 minutes to give the battery any meaningful charge and get it back to a safe level for your next start.

If The Battery Is Totally Depleted

A car battery is considered completely discharged when the voltage drops below 12 volts. In this case, you can’t and must not try to charge the battery using your alternator as above, since the alternator was only ever designed to charge a reasonably healthy battery. completely recharge a dead battery. 

Driving your vehicle to get the alternator to restore such a completely discharged battery means the alternator is forced to overwork to revive the dead battery as well as powering other crucial components. This will damage the alternator, and what’s more, the alternator cannot provide sufficient power to recharge a completely depleted battery, so it’s only undercharging the battery. Undercharging will shorten the battery’s lifespan, while it won’t be able to effectively keep the charge provided by the alternator.

While using the alternator to recharge a completely dead battery is both inefficient and detrimental to both parts, you can try three methods below to safely get some juice out of your dead battery:

Use A Jump starter/ Dedicated Battery Charger: The safest way to revive a seriously depleted battery is to connect it to a jump starter or a dedicated battery charger either before or immediately after a jump-start. Both of them are special charging devices designed to safely restore a 100$ discharged battery back to full charge. Most of the time, you won’t have to remove the battery to get it revived.  

Note: Don’t shut the engine off, since the dead battery won’t accept a charge. Also, in the case the battery freezes, do not attempt to jump start it as the battery housing will bulge and can explode. Thaw it out first.

Distilled Water: If the battery acid or electrolyte level is low, a common trick is to add some distilled water to fully-submerge the plates again, which will enable a bit more area for chemical reaction to occur. Adding distilled water might be enough to give the engine a few more turns.

Epsom Salt: This might sound surprising, but it is basic chemistry. Epsom salt is something widely sold in grocery stores and commonly used for relieving muscle pains and constipation. It is magnesium sulfate or MgSO4 and is a strong acid. When the battery acid level is low, you can add this strong acid together with distilled water to the electrolyte mix to tip the chemical balance, which might provide enough charge to give the engine a few more turns. Dissolve Epsom salt with warm distilled water at a 1:3 ratio, then add to each cell until ¼” to ½” of the plates are submerged.


When A Dead Battery Cannot Be Revived Anymore

Even when you can get your car back on the road after a jump start or after recharging your dead battery with a dedicated charger, the accumulation of hard sulfation is irreversible and will lead to the ultimate death of the battery, when its ability to hold a charge is zero.

Also, when a battery is left dead for an extended period of time, the lead sulfate will form hardened crystals buildup that can’t be broken up by the alternator, a jump starter or a dedicated battery charger. The only option then is to replace the battery altogether.

A battery meets its ultimate death when the multimeter or voltmeter returns a reading of about 10.5 volts or below. At this point, the lead plates are almost entirely coated in lead sulfate. There’s hardly anything left for chemical reactions to occur, thus it may no longer be possible to restore the battery back to full charge, or if it’s possible, a full charge will not last long, or readings might show a full charge but in reality the battery cannot reach full charge anymore.

Prevention Is Key: Do Not Let Your Battery Die Completely

To prevent hard sulfation, hard starting problems and premature battery replacement, you need to pick the right battery and take appropriate preventive measures.

Use A Float/trickle Charger When Your Car’s In Storage

As above, a discharged battery should be recharged immediately, and leaving a battery discharged or dead for a long time will kill it altogether prematurely. This means if you need to store your vehicle away or let it sit idle for an extended period, you will need to maintain the battery’s charge during that period.

To do this, you’ll need to buy a float charger, which is also known as trickle chargers, storage chargers, or maintenance chargers. This type of charger prevents the battery from a natural process called self-discharge, in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes or any external circuit. A float charger will supply a charge rate that is equal to the battery’s self-discharge rate, thus keeping your battery at full charge. 

Most trickle chargers have built-in circuitry to prevent overcharging so you can leave the charger on during the whole storage season. That said, some models do not and can damage a battery by overcharging it, and regardless of how high-tech your float charger is, you should always  periodically take a look to make sure that everything is still in good working order.

Regularly Check For Corroded or Loose Battery Terminals

Over time, battery cables and terminals are prone to corrosion. In addition, the terminals fitting can become loose. These will impede the alternator’s ability to charge the battery, thus it’s basic battery maintenance that you should regularly inspect the battery to make sure it’s intact. 

Fortunately, you can easily clean your car’s battery terminals with a commercial solution and a soft bristled brush, and a simple yet effective tip to protect against corrosion is to add a little Vaseline on the terminals. Another easy solution for preventing corrosion is to apply liquid electrical tape to create an airtight seal.

Choose Weather-Resistant Batteries & Protect Them From Extreme Temperatures

Extreme temperatures can cause irreversible damages to your battery and kill it off completely. According to AAA’s Automotive Research Center, a car’s battery is weakened by about 60% at 0°F and at 32°F it loses 35% of its strength. 

Because the temperature has a significant impact on your car battery, you should choose a battery appropriate for your local weather conditions. It’s best to consult your owner’s manual as well as a certified mechanic. Batteries specifically made to withstand extreme heat are often labeled “S” or “South” while cold-weather batteries are often labeled “N” or “North”. 

For cold climates, you should choose a replacement battery with a higher Cold Cranking Amps (CCA) rating than the old one to ensure better performance. CCA is a rating used to measure a battery’s ability to start an engine in cold temperatures. Typical CCA readings for a car range from 350 to 600A. The standard recommendation is a battery with at least one CCA for every cubic inch of engine displacement (CID – not liters). For diesel engines, you need at least two CCA for every CID.

As a safety cushion, if you live in an extreme cold climate, add a 20% buffer of the cubic-inch displacement to the CCA. Therefore, a 350 cubic-inch displacement engine requires at least 420 CCA minimum (350 + 70).