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How to Know When It’s Time for a New Car Battery

How to know when its time for a new car battery header

By Andy Jensen on July 6, 2021 in Safe Driving

Imagine you cut it close one morning. You need to hurry, or you’ll be late for work. You rush out of your house, get in your vehicle, turn on the ignition — and hear nothing. Your battery is dead, and you can’t use your USB charger to get it going again.

While it seems like a dead car battery comes out of nowhere, you may be able to prevent one by watching for a few signs that indicate the battery is about to fail. Read on to learn which signs to watch for, how to maximize your battery’s life, and when to replace your car battery.

Why Batteries Fail

Like any vehicle component, from the air filter to the fuel pump, car parts wear out and eventually need replacing. You probably didn’t do anything to cause your battery to fail; they simply wear as they age. The liquid electrolyte mix and metal plates inside are vulnerable to dilution or corrosion, and they slowly lose the ability to hold a charge. Usually, a battery will last three to five years. If you’ve had yours longer than that, consider replacing it.

If your battery isn’t past its prime, you have some control over how long it lasts. Beware of these factors, which can negatively impact battery life.

  • Excess vibrations

If you frequently drive on rough roads or have a worn motor mount, your battery may suffer excessive wear and tear.

  • Extreme hot and cold temperatures

Summer heat is particularly tough on car batteries and can accelerate battery failure.

  • Continual under-charging

When you never fully charge the battery because of a failing alternator or because you have a short commute, you can damage the internals, limiting how much charge your battery can store.

  • Full battery drain (zero charge)

Letting a drained battery sit can permanently damage it. If you say, “I’ll get it this weekend,” your battery may go from drained to broken.

  • Not driving often

Most modern vehicles pull tiny amounts of charge for electrical components, even when switched off. Your battery charge can go to zero in just a few weeks.

Failing Battery Symptoms

Look for these signs to determine if your battery is showing signs of aging and wear.

  • Slow-to-start engine

This symptom means the battery did not retain enough charge to power the starter. With less power, it needs more time cranking to get the engine started. If you used to see instant starts but now it takes 2 or 3 seconds, treat it as a warning sign.

  • Dim headlights

With a failing battery, the rest of the electrical system will have trouble too. You’ll probably first notice that your headlights are dimmer than usual when starting the engine or when it idles. Also, check the overhead light when a door is open. Reduced lighting in the interior, which is easily noticeable at night, means the cabin lighting isn’t getting enough power.

  • Check-engine light

A low battery should activate a battery warning light on your dashboard gauges, and it can also set off the main check-engine light. The reason? Any system using electrical power, from the main computer to the power windows to the transmission, may receive insufficient power, causing it to malfunction or operate slower.

  • Corroded battery terminals

Pop the hood and examine your battery for a white, powdery, corrosive buildup on the terminals. Small amounts of corrosion aren’t always a sign of a bad battery (more on that below), but heavy corrosion on the terminals is a warning sign.

  • Cracked or swollen battery case

This symptom indicates a failing battery and is not a normal operating condition. A cracked case allows the electrolytes to leak out, while a swollen battery case may point to massive overcharging, complete discharging, or severe damage to the internal battery plates.

  • Backfires

A backfire is an uncontrolled explosion of fuel and air, which can severely damage an engine. Backfires are rare in modern cars, but they can happen if your alternator fails and kills your battery while driving. The battery’s charge quickly runs out, and the computer is unable to control modern fuel injection without power, leading to a backfire before the engine shuts down.

  • Rotten egg smell

Most drivers know this stinky situation can be a symptom of a failing catalytic converter. However, the same chemical that causes that stink – hydrogen sulfide – can cause a smell beneath the hood too. Often caused by over-charging, the stinky gas is a sign to disconnect the charger and come back once your engine airs out.

How to Determine If You Need a New Battery

Technicians at the dealership service center and auto parts store will probably say you need a new battery, but do you? Here are some quick DIY steps to determine if it’s time to buy a new battery. Use a multimeter to determine the battery voltage. Even the cheapest multimeter from the dollar store is a useful tool, and here it can help determine if you need a new battery or if you can save your current one.

Turn on the multimeter and set it to DC at the 20-volt setting. Connect the red lead to the positive battery terminal. Then attach the black lead to the negative terminal. The display should read at least 12.4 volts. A lower reading means the battery needs a charge. You may have a bad battery. Charging only takes a little bit of time and costs almost nothing, so give it a shot first.

Charging an Empty Battery

You have two main options for charging a dead car battery. If you have a few hours and a battery charger, go that route. Connect the leads, red to red and black to black, and use the slowest setting. This trickle charge is like connecting your smartphone to a slow-charging power source, such as a laptop. The slow charge provides a jolt of power without further damaging the battery if it’s totally drained. Charge it until it measures at least 12.4 volts on the multimeter.

If you don’t have a battery charger, your other option is a jump start. Jumper cables, or jump-start packs, provide the instant burst of power your vehicle needs to start. The idea is to provide enough power to start the vehicle, then let the charging system recharge the battery. Once the engine starts, drive your vehicle for at least 20 minutes to give the alternator time to work. Measure the voltage again after the drive.

If your battery only needs a charge, you should be good to go at this point. If you still see signs of battery failure, then it’s time for a new battery.

Extend Your Battery’s Life

If you squeaked by this time but want to prevent early battery failure, here are a few things you can do that help extend the life of your battery. Batteries are expensive, so give these tips a try.

  • Clean the battery terminals

Minor corrosion is normal as the battery operates, and buildup increases during tough conditions such as extreme hot or cold temperatures. Keep the terminals clear of any grime that can disrupt the flow of electrons. Corrosion is easy to clean off by using an old toothbrush, water, and baking soda. Auto-parts stores sell cheap dielectric grease to help solidify the electrical connection.

  • Avoid extreme temperatures

Park in the shade or a garage when you can to keep the temperatures down.

  • Drive regularly

The cycle of discharge and recharge extends battery life more than sitting in the garage. If you’re retired, work from home, or have more vehicles than drivers, fire your car up once a week for a leisurely drive.

  • Avoid short trips

A two-mile drive is harder on your ride than a 20-mile trip. The battery can’t fully recharge during short trips. For example, the starter may need 20 percent of the battery’s power to start the engine. If you only take two-mile trips that recharge 5 percent back to the battery, eventually the short trips will drain the battery.

  • Don’t use accessories when the engine is off

The radio, air conditioning, navigation, and other comfort-and-convenience features need electric power. Without the engine running, the electrical power comes entirely from the battery and can quickly drain it.

  • Warm up your car before you turn on accessories

Once you start the engine, run the vehicle for a few minutes before you use any accessories. You’ll drain the electrical system less and allow the battery to recharge more quickly.


Is your battery drained or dead? With the tips above, you’ll be able to find out. If you look for signs of failure and take easy steps to diagnose your battery’s condition, you should be able to spot a failing battery before it ruins your day.

Andy Jensen is a consultant for Say Insurance. He's an automotive enthusiast writer specializing in new and used models, industry tech and trends, and the car culture that surrounds it all. After receiving a Bachelor of Journalism from the University of Central Oklahoma, he decided to write about cars instead of getting a real job. He’s written for Jaguar, Volvo, Ford, Advance Auto Parts, Haynes Manuals, and others. His project car probably isn’t running.