Rick's Free Auto Repair Advice

Car Battery Keeps Dying

Car Battery Keeps Dying — Most Common Causes

If your car battery keeps dying and you have to jump start your car to get it started you’re got an underlying problem that needs to be fixed. Here are the most common causes for a car battery that keeps dying.

The battery is old and worn out

Car battery life is typically around 4-years. If you’re

car battery keeps dying

Solar BA9 battery tester

near that point and your car battery keeps dying, chances are the cells inside the battery have deteriorated and can no longer hold a charge. Or, they’ve shed plate material and that’s created an internal short that prevents the battery from holding a charge.

Modern car battery testers can diagnose the condition of your battery without removing it from the vehicle. Most auto parts store will perform the test for free.

You leave your car parked for long periods and your car battery keeps dying

All batteries self-discharge when left unused. Car batteries are no different. In warm weather, a car battery can self-discharge as much as 1-2% per day, and that’s when it’s disconnected from your vehicle. When connected, the computer power draw, along with the self-discharge can run a battery down in about 4-6 weeks.

When you leave a car battery in a discharged state for long periods, sulfation occurs, permanently damaging the battery.

In addition to forming irreversible sulfate crystals on the plate, letting a car battery sit for long periods also results in acid stratification, when the battery acid, being heavier than water, settles to the bottom of the battery where it degrades the lead plate material.

During Covid, more car batteries were destroyed from non-use than any other cause.

You drive short distances and your car battery keeps dying

Every time you start your engine, you drain power from the battery. If you then drive a short distance, the charging system doesn’t run long enough to replace all the power lost during the start-up. If you drive a short distance and run any electrical accessories like the heater, defogger, heated seat or headlights, you drain considerably more power out of the car battery. The result is a constantly discharged battery.

Just for reference, it takes at least 30-minutes of highway speed driving to recharge a discharged battery. If you think you can let the engine idle to recharge your battery, think again. It takes almost 4-hours of idling to recharge a dead battery.

Your battery terminals are corroded

Corrosion between the battery terminal and battery

corrosion on these battery cable

Look at the corrosion on these battery cables. And you wonder why it won’t start?

post creates electrical resistance that prevents your charging system from fully recharging the battery. So, no matter how often you drive or how long you drive, the corrosion reduces the amount of charging the battery receives. Corrosion also puts an extra burden on the alternator, causing it to fail early. Cleaning your battery terminals is the best thing you can do to keep your battery in tip-top shape.

You have a parasitic battery drain

All modern cars have computers that draw a small amount of current at all times. The keyless remote system, for example, must be powered at all times so it can receive the “door unlock” command from your key fob. The other computer modules in your car are designed to go enter a low power “sleep mode” when they’re not in use. It often takes up to 45 minutes for all computers to shut down after you’ve shut off the engine. In a module doesn’t enter sleep mode and it continues to draw full power, it can run down your car battery overnight. That’s called parasitic battery drain.

If you’re handy you can diagnose this yourself. See this post. Otherwise, take your car to a shop for a professional diagnosis.

Your charging system is failing

Alternators have a limited life span. As mentioned above, you can hasten the demise of your alternator by not cleaning the car battery terminals. Alternators fail due to overheated or shorted diodes, worn brushes, deteriorated windings, or electronics failure.

You leave lights on and your car battery keeps dying

Let’s take a look at how much power gets drained from your battery when you leave your lights on:

Parking lights: 4 side marker lights, two from parking lights and two rear parking lights. Total draw 2.45-amps (approx 30-watts). If your car battery is rated at 50-amp hours, it will be completely dead in 16.6 hours.

Headlights. Side marker lights, parking lights and headlights = 8.3-amps (140-watts). At 50-amp hours, the battery will be dead in 3.57 hours.

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Posted on by Rick Muscoplat


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