Car Battery Keeps Dying but Alternator is Good? [Here’s What To Do]

Have you ever been stranded on the side of the road with a dead car battery, only to be told by a mechanic that your alternator is just fine?

It’s such a frustrating and confusing situation, but don’t worry, we will help you resolve the issue. 

In this blog post, we will help identify the common reasons your car battery may keep dying even though the alternator is functioning properly.”

car battery and alternator

Why Does my Car Battery Keep Dying but the Alternator is Good?

1. Weak/Old Battery

A weak or old battery is a common reason your car battery will keep dying even when you have a good alternator.

The typical automotive battery has a lifespan of 3-5 years, which means, the older the battery, the lower its capacity to hold a charge. 

A faulty battery can disrupt practically every electrical component in your vehicle, including the charging system, and this could result in dimmer headlights and difficulties starting the vehicle.

Also, weak batteries might potentially harm your starter motor and alternator. Because when the battery’s power is low, the starter motor and alternator require excessive voltage to compensate.

Symptoms of a Weak/ Bad battery

  • Dim Headlights
  • Slow Engine Crank
  • Clicking Noise When Trying to Start The Car
  • The Engine Backfires
  • Smell Of Sulfur
  • Swollen Battery Case

2. Corroded Battery Terminals

Corroded terminals can cause your battery to die, preventing the vehicle from starting. As a result of the hydrogen gas generated by sulfuric acid, the battery tends to deteriorate and when the gas reacts with the surrounding atmosphere, it creates a corrosive environment.

Battery terminal corrosion typically occurs on the negative battery terminal, which is a sign of undercharging the vehicle’s battery.

Battery corrosion can also cause a slew of other car battery issues, such as damage to the vehicle’s chassis, electrical wiring, air conditioner lines, and other components.

Proper battery corrosion prevention is vital to the battery’s and vehicle’s health.

How to Clean a Corroded Battery

Step 1: Disconnect the battery cables

To begin, disconnect the battery lines from the battery. Begin with the negative battery cable, which is usually denoted by the negative symbol (-), its acronym (NEG), and/or being black.

Next, disconnect the positive battery cable, which is usually denoted by the positive symbol (+), its abbreviation (POS), and/or the color red.

Step 2: Examine the Battery Cables

Check the battery cables for wear and tear or corrosion. Examine the insulation for signs of dryness, cracking, and peeling. The plastic or rubber sleeve on the cable serves as insulation.

When exposed to the outdoors, the copper stranding restricts current flow and becomes brittle. A typical cause of a vehicle not starting is frayed battery wires.

If there is any damage to the battery cable(s), replace them.

Step 3: Remove and Neutralize Battery Corrosion

Spray a battery cleaning product anywhere there is battery corrosion on the battery or battery wires.

Step 4: Dry and Polish Battery Posts and Terminals

Once you remove the battery rust, dry the battery, battery posts, and battery terminals on the battery wire.

A microfiber cleaning cloth is an excellent option. Use a battery terminal brush to remove any remaining residue.

Step 5: Install Anti-corrosion Pads

These pads are battery terminal protectors used on each battery post. It’s best to soak each one in a corrosion-preventative chemical.

Step 6: Connect the Battery Cables

Reconnect the battery cables. Reconnect the positive battery cable first, followed by the negative battery cable.

3. Parasitic Drain

This is a continuous and abnormal discharge of power that occurs, even after the engine is shut off.

A parasitic drain occurs when the electricity produced by the automobile battery continues to operate a variety of gadgets and accessories.

These might range from the computer in your engine to your alarm system or internal clock.

Several factors, including short circuits or electrical devices that stay active, contribute to serious parasitic battery depletion. 

To diagnose a parasitic drain, you need to carry out a parasitic battery drain test with a digital multimeter. This can help you determine how much draw is being placed on your battery. 

How to Check Parasitic Drain

  • Appropriately set up the multimeter. Before then, make sure your battery is completely charged (12.6 volts).
  • Turn off the engine and take the keys from the ignition. Turn off all lights and leave the vehicle for around 5 minutes. This will give your vehicle enough time to shut down all of its systems before checking to see whether anything is still drawing electricity.
  • Unplug the battery’s negative terminal. Always check for a parasitic draw on the negative circuit to avoid shorting out anything.
  • Connect the black lead of your multimeter to the negative battery post and the red lead to the disconnected negative terminal.
  • Check your multimeter. If you have a modern multimeter that automatically determines its range, check to see what unit your reading is showing. If it says “MA,” it’s in milliamps; if it just says “A,” it’s in amps. Any value above 100 mA indicates a parasitic demand (1 amp = 1,000 milliamps).

4. Leaving Headlights Illuminated Overnight

The battery powers the onboard electronics like headlights and dome lights. Note that it operates even when you turn off the engine. This indicates that the battery may be drained if certain accessories are used excessively.

When the number of times you turn on the headlights reaches a limit, they become the never-ending culprit. This condition involves seemingly benign actions that take place in a short period of time, such as going to the grocery store or taking out coffee.

Meanwhile, leaving the dome lights on overnight will almost certainly drain a weak battery. As a result, you should inspect these areas in the dark in order to identify the signs with ease and accuracy.

5. Poor Battery Connection

Poor battery connection is another typical issue that can lead to a host of issues, such as loss of power, engine misfires, and even total electrical system failure.

When your battery connections are not properly fixed, the alternator would not be able to recharge the battery and it will lead to it dying. 

Moreso, despite the potential damage they can cause, many people are unaware of the dangers of poor battery connections and how to fix them.

Therefore, if you have no knowledge of how to properly connect your car battery, it is necessary to contact a mechanic.

Read: Idle High in Park?


When your car battery keeps dying but the alternator is okay, it simply shows it’s a battery problem. The most likely cause is a faulty/bad battery.

If your battery can’t hold a charge, it doesn’t matter how much electricity your alternator is pouring into it, it will keep dying.

Another possible cause is corroded battery terminals, which typically occur on the negative battery terminal.

Also, it could be that your battery connection is not properly connected and, as a result, your alternator would not be able to recharge the battery.