Why Did My Car Battery Die?

A car battery is the most dramatic of all car parts. That's what guitar-strumming comedian Demetri Martin says. You see, other things just break or quit working.

Not batteries. They die.

Car batteries die when they weaken from too much cold, heat, drain, corrosion or vibration that they don't have enough electrical power to crank the engine.

No matter how tough they look, car batteries are sensitive electrochemical devices. They're affected by anything that would disrupt both electrical systems and chemical systems.

Why does your car battery keep dying? An exact diagnosis takes a trained automotive technician. (And we know of a reliable auto tech at a location near you.)

This article shows you the main reasons a car battery dies and which factors might cause your car battery to die so soon. But before we get into the usual suspects, let's talk about the typical lifespan of a car battery.

How long do car batteries usually last?

A car battery usually lasts three to five years. Yours can last longer if you keep it fully charged and if you guard it from the car battery killers.

It is true that car batteries wear out over time. It's also true that a dead car battery may be a sign of a deeper issue in your vehicle. Your alternator may be on its last legs. The starter might finally have given out. There may be a broken wire draining the battery. Your mechanic can diagnose those by looking for volt drops.

Aside from any engine issues affecting your car battery, you can expect three to five years from any car battery.

Let's give you a rundown on how each car battery killer works.

Cold suppresses a car battery's power until it's dead.

Remember this from high school chemistry? Cold slows down chemical reactions.

The electrical power in your car battery is 100 percent chemistry.

Batteries work best at 80 F. A fully charged battery can start a car engine all day at 80 F. When you start the ignition, you start a complex chemical reaction. The car battery's lead plates, the liquid electrolyte and chemical additives become free to interact. Inert molecules shift around, sending a bunch of electrons jumping up from the battery terminals, up the wires and into your starter.

Cold temperatures slow that down. A lot. Let's take the same car battery and, instead of a balmy 80 F, drop the temperatures and see how it performs. At 32 F, the chemical reaction would have to be much stronger to produce enough of those electrons to start your engine. Nothing changed about the engine. Nothing changed about the battery. Only the temperature changed.

Battery performance is worse at 0 F. The battery has to work twice as hard. The chemistry reaction must be twice as strong to produce an electrical charge to start the same engine. That's why the cold cranking amp (CCA) rating measures the battery's performance at 0 F. The CCA rating shows how strong the new battery should be at 0 F, which is one of the hardest environments for a battery.

That's why a car battery often dies on cold mornings. It tries to produce enough power but still can't start the engine.

This is also why you can buy a battery blanket at an auto parts store, especially if you live in an area with heavy snow and extremely cold winters. Yes, it is exactly what it sounds like. Look up “battery blanket.” You'll find sturdy heating pads shaped to wrap around a car battery. The blanket keeps the car battery warm for hours and hours if you put it on when you turn off the engine. A battery that's even one or two degrees warmer than the surrounding air can mean the difference between a normal morning or getting a jump-start.

Cold temperatures also make it hard to recharge a car battery. Short trips drain your car battery, and if you never drive long enough for your alternator to recharge it, your car battery will grow weaker and weaker every time you start the engine. A full recharge protects your car battery. Leaving a car battery drained can damage it and make it more vulnerable to extreme cold.

A drained car battery can't produce a strong enough reaction to start your engine. A drained car battery can even freeze solid. As a car battery uses its electricity, the liquid electrolyte inside becomes more like water. By the way, if your car battery freezes solid, do not jump-start it. Get help.

One of the best ways to protect your car battery from the cold is by keeping it fully charged. You will need to leave the battery charging a couple extra hours if it's cold.

Because the cold slows down the battery's chemistry.

Heat speeds up the internal corrosion that chips away at a car battery's power until it's dead.

If extreme cold kills batteries, then heat should be safe for car batteries, right? Well, it's possible for your car battery to get too much of a good thing.

Car batteries work best at 80 F. If it gets hotter than 90 F, the chemistry holding the electrical charge gets a little too active. Then it starts to degrade the sensitive components inside the car battery.

Just as cold slows down chemical reactions, heat speeds them up. That means two things for your car battery. First, it's really easy to produce the reaction you need to start your car. Second, your battery is slowly corroding its ability to store power.

It's a different corrosion than what you might see at the battery posts. Here's the nitty-gritty: The liquid electrolyte inside the car battery is a corrosive acid surrounding lead sheets and a coating on those sheets. When you start the car, the acid merges with the lead—freeing up the electrons your starter needs. However, until you turn the key, the electrolyte is still a corrosive acid. And every so often, a molecule of that liquid nibbles away at the lead. Or at the coating. Or both.

The result is brittle grit that crumbles to the bottom of the battery.

Every ounce of that lead and its coating is where your car battery holds electricity. Less lead means less electric power it can store. That's the car battery's capacity. It's still fully charged, and yes, it can still start your car. Extreme heat hides the weaknesses in your car battery. However, it is permanently losing years of its total lifespan.

Imagine your phone battery at 100 percent charge in your hand. Now imagine it physically shrinking. It is still fully charged—but you're not going to expect it to run as long as before. Then one day, it's going to be too small to work.

A car battery lasts three to five years, but it does wear out over time. Colder than 80 F, a car battery's sensitive components are relatively safe from its acid. However, the acid chips away at the lead when temperatures are in the 80s or hotter.

Extreme heat speeds up your car battery's natural aging.

Compared to the other battery killers, extreme heat is the most damaging and the sneakiest. It typically works with one of the other battery killers:

• A couple of intensely hot summers in a row can shrink your car battery's capacity enough for one winter's cold snap to overwhelm your car battery.
• Or it breaks down the internal components enough for a few intense vibrations to break the lead plates.
• Or the heat shrinks how much power the battery can hold—while a power drain uses up what little power your car battery has.

Extreme heat is mean to your car battery.

It's also fairly easy to avoid. Park your car in the shade.

Power drains deaden a car battery's ability to recharge.

Everyone's got a story about leaving a car's headlights on—and the emergency rush for a jump-start right after.

Car batteries are meant to start cars. One big, powerful, 30-second burst of energy and then about 20 minutes of a comfortable recharge from the alternator. Regular car batteries are not designed to run a sound system and recharge your laptop with the engine off. (An AGM battery is powerful on a whole other level.) The onboard computer takes a small drip of power to save its memory, but it's not much of a drain on your battery, unless you leave the car parked for too long.

A normal power drain for most vehicles is about 20-50 milliAmps when the engine's off. Or greater if your vehicle is newer than 2009. According to a study of electrical vehicle demands from battery manufacturer Clarios, the number of onboard electronics tripled from 2009 to 2018. And you might recognize some of those:

• Automated safety features
• Dashboard touch screens
• Collision mitigation braking
• Start-stop engines
• Sensors reading the road and engine
• Wireless Internet or Bluetooth connections
• USB ports for device charging

These are all part of the modern driving experience—and the vehicle models that use these do require different batteries such as an AGM or an EFB battery to support the heavier load whether the car engine is on or off.

What might drain a car battery too much? Any substantial power usage when the engine is off, such as

• Charging your phone
• Using any car electronics for any length of time
• Car key fobs close enough to repeatedly signal the parked car
• Interior lights or courtesy lamps left on
• Any accessories or customizations with lights or wireless connections
• Even wet grime on the top of the battery. It could conduct a slight current

A qualified technician can diagnose electrical issues and help you find whatever might be draining your car battery.

Now, the problem with draining a car battery to 50 percent is worse than you think.

Yes, you have an immediate problem because your car battery doesn't have enough charge to start your car. The deeper problem is how long it takes you to fully recharge it.

Leaving a car battery drained for just a few hours will leave permanent damage.

Think back to the battery chemistry we've covered. Your car battery is lead plates, coated with sensitive materials, sitting in cups of liquid electrolyte. When you start the car, the acid merges with the lead to become lead sulfate—freeing up the electrons your starter needs. Then, recharging the battery separates the acid from the lead. But what if recharging doesn't come? The lead sulfate hardens in place. That process is called sulfation, and it's not good for car batteries. Sulfation toughens the battery materials against any chemical changes and destroys active materials.

Then the current can't pass through those dead spots when recharging electricity does come. It's a part of the battery's lead that is now permanently drained.

With less active material to start the engine, the car battery will struggle for the rest of its time under the hood — until one day the engine needs more power than the battery can give.

Then it's dead.

Corrosion puts new resistance into connections until the battery is so tired, it dies.

This is the spiky, intimidating battery killer you might see on top of your battery if you lift the hood. Corrosion gets a foothold from heat and grime on top of a dirty battery. Corrosion usually frames another usual suspect for its dirty work.

Corrosion causes electrical resistance. If there's one thing your car battery doesn't need, it's something slowing the flow of electricity.

All metal that carries an electrical current will corrode. However, when a little moisture and grime show up, corrosion builds. It's using electrons from your power supply into a non-conductive gunk you'll have to eventually clean off.

Clean off the corrosion regularly. A little electrical resistance can cause big problems.

Namely, voltage drops.

Your 12V car battery runs with 12.77 volts if it is healthy, sending 500 amps to start your engine. If a mechanic measures your battery and sees it only has 12.5 volts, they might think they need to recharge it because it is so weak.

Think of volts as a minimum speed limit for electricity. If there's no cars broken down on the highway nor car accidents, then nothing interrupts the flow of traffic. Electrons can get to work on time.

A voltage drop happens when corrosion gets in, molecule by molecule, between the positive terminal and the positive cable and causes small breakdowns on the 12V electricity highway. Instead of sending all 12 volts, your healthy car battery winds up pushing 500 amps with just 11 volts to the starter.

Which means your car might not start at all. Or, what's more likely, your car does start but with a bit more effort than usual. When the alternator tries to recharge your car battery, the small dosage of fresh electric current just doesn't fill it up to 100 percent. Then you're facing a power drain problem.

Corrosion eats more than your car battery's electrons.

It can actually eat the clamp connecting your battery to the car. If the clamp on your battery post is thin enough, corrosion can chew right through it to where the electrical connection does stop. Battery posts themselves are thick, so corrosion would have to work a long time to get through those. However, the clamps or spliced wiring are potential victims to hungry corrosion.

The best way to avoid corrosion is with a little TLC on your car battery:

• Clean off any dirt or grime you see on the top of its case.
• Use baking soda and distilled water to eliminate any built-up corrosion.
• Use a corrosion preventative spray on clean terminals.

Vibration knocks once-active material loose and even bends the lead plates—prematurely ending your car battery's life.

Vibration is the most common way to kill a car battery.

Of all the ways your car battery can die, vibration is the least sophisticated. Shake any car battery long enough and hard enough, and you'll damage its internal components.

The everyday rumble of your car engine isn't going to do the job (unless it isn't securely tied down in the engine.)

The lead in your car battery is thin. It's formed into thin sheets, or lead plates, that hang from the top of the battery case into the cups of electrolyte. The sheets of lead don't touch the sides of the battery, they don't touch each other and they don't touch the bottom. However, they are hanging in the liquid. If vibrations shake it the right way hard enough, the plates may touch something they shouldn't. Then your car battery will short circuit.

Off-roading, a car accident or dropping a car battery may vibrate the lead plates enough to bend or break the lead plates loose.

However, those kinds of shakes are rare. More common is a big pothole, 10 minutes on a bumpy road or hitting a speed bump too fast.

Those vibrations may not dislodge a whole lead plate from your car battery. Instead, they knock free the sensitive coating or a chunk of still-active lead that was corroded loose. With less lead to work with, the car battery loses the capacity to hold and deliver electrical power.

Now that the battery is severely weakened, any of the other battery killers—a frigid winter morning, a power drain from charging your laptop or a corroded terminal—will have an easier time killing it.

So, who's the culprit in this whodunit? They all did it.

Cold, heat, power drains, corrosion and vibration are the five battery killers. And they tend to work together. Your car battery is a sensitive electrochemical device stored in a turbulent environment, working in the least forgiving conditions.

Heat speeds up corrosion in the car battery while corrosion chips away at its connections to the engine and alternator. Vibration shakes off once-useful materials, leaving the battery too weak to make a big enough reaction on a frigid morning. Power drains rob the car battery of its total power. Extreme heat shortens its lifespan. Then a cold snap may suffocate the battery enough to kill it.

Yet, your car battery is strong enough to work reliably for years.

So, how does a car battery die?

Suddenly, usually with no warning.

Over the decades, car makers have made small, powerful engines that are easier to start. Drivers back in the 1980s or the 1990s might spot a weak car battery early. A slow or sluggish start on a warm day would trip your battery warning light. If you ignored it, well, your car would be dead after a day or two of that.

If you're driving a 2010 or newer model, sophisticated electrical systems and easy-to-start engines mean that a weak car battery can carry on—getting weaker and weaker as time goes on. The only time you would see the car battery warning light is after your car battery died.

What can you do to prevent your car battery from dying? Get a battery test from a reliable technician or at an Interstate All Battery Center^® location.

A battery test does more than check if it's charged up. Your test will identify issues, show where your car battery is in its total lifespan and even give you a good estimate or an idea of when your battery could fail. A test takes 2-5 minutes and will tell you if your car battery has a few years ahead or just two weeks.

Get a battery test before winter and another before summer. Or get a battery test with every oil change.

Follow up with battery tests regularly. You may be in time to prevent your next car battery's untimely death.