Car Won’t Start After Replacing Battery? (10 Causes)

Nothing’s more frustrating than turning the key and hearing nothing but silence from your car. You just replaced the old battery hoping it would get the engine humming again, but still no luck.

In this guide, we’ll walk you through some of the most common reasons a car won’t start even with a new battery and how to pinpoint the real culprit so you can get back on the road.

Causes Of Car Won’t Start After Replacing Battery

Here are the causes of the car won’t start after replacing the battery.

• Bad alternator
• Loose battery connection
• Corroded Battery Connectors
• Faulty Starter

1. Loose Battery Terminals

Battery connections provide the vital link between the battery, load, and the charging system. If the connectors to the posts of the battery are loose or corroded, they can cause your car not to start.

Checking the connections of the battery should be your first step before moving further to inspect other parts of the car starting system.

A loose battery connection will not be able to supply the proper current. It will also create sparks on regular basis near a battery, resulting in the melting down of the battery post.

For loose battery terminals, make sure that the the nut of battery terminal is properly tightened with a wrench. Now, it depends on which type of terminal you have.

Also, make sure the battery terminal is fully seated against the post of the battery. I had this problem when I didn’t push the terminal down far enough over the post.

You can use a rubber mallet to lightly tap the battery terminal. If you hammer hard, it could damage the battery posts and cause internal leakage to the battery.

2. Corroded Battery Terminals

The terminals of a car battery corrode over time due to the acidity of the battery and the high voltage of the battery. As the terminals become corroded, they can no longer carry the voltage to generate the current that powers the car.

When checking the terminals, you will need to remove the negative terminal first. The negative terminal of the battery shares ground with the car chassis, engine block, and other metal parts.

If you first remove the positive terminal of the battery, the chances of a spark are more if this terminal touches the body through the metal spanner or wrench, it will produce a big spark.

How to fix?

After removing the terminals of the battery, use a small wire brush to clean the dust and scrap the corrosion particles. After that, clean the battery terminals with a mixture of water and baking soda.

To prevent corrosion on the terminals, apply a thin coat of petroleum jelly to the battery terminals after reconnecting the battery cables.

When installing battery terminals after cleaning them, make sure that the positive terminal is connected first before the negative terminal.

3. Damaged Battery

If you have got a cheap aftermarket car battery, chances are that it may have damaged the battery.

To check if the car battery is fine, you have to test on the battery posts with a voltmeter. Have someone turn the key and try to start the engine, while you put the voltmeter probes on the battery posts.

If the battery voltage drops below 9V when trying to crank the car, the battery is run down or defective.

4. Damaged Battery Connections To Ground and Starter

In engines, current flows out of the battery in one direction via its positive terminal and back to it via its negative one. 

Now, take a voltmeter. Connect one probe with the negative terminal of the battery and the other on the engine block or chassis.

If the connections are fine, there should be around 0.2v recorded on the voltmeter when trying to start an engine.

If you can see any voltage, it means battery ground connections are damaged. You should check your owner’s manual to find all grounded connections on your engine. You have to visually inspect them for any corrosion.

In some engines, there is also a ground strap connection between the car body and the engine. Its ends are usually mounted on the transmission and car body. If the ground strap is weak or torn in any way, it could also car not to start.

Now, repeat the test by connecting a probe of the voltmeter with the positive terminal of the battery and another probe with the solenoid terminal of the starter.

Ideally, there should be no voltage drop across the battery positive terminal and starter solenoid terminal i.e. there should be negligible resistance in the circuit. So, if the connections are good, the voltmeter will show a voltage of less than 0.2V.

Check out the below video for a better understanding:

5. Malfunctioning Alternator

A malfunctioning alternator can also cause your car not to start. You replaced the battery of your car because you thought that the battery of your car was damaged.

But, the chances are that the alternator has gone bad that is not charging your car anymore.

In engines, an alternator converts the mechanical energy of an engine into electrical energy. The alternator is just like a generator that is run by the crankshaft via a serpentine belt.

Also Read: New alternator new battery still not charging

How to diagnose?

If you want to check the alternator, a quick diagnosis would be to jump-start the car. Then immediately remove the jumper cables with the car running. The car should remain running.

If the car dies out shortly after removing the cables, it means the battery is not being charged. A bad alternator can also cause cells in the battery to fail entirely, making the battery weak and it won’t ever fully charge. 

Now, if it’s verified that the car is only starting for a while when the battery is jump-started, it means that the alternator might be bad.

For a proper test of the alternator, your engine should start. When you start the engine, the voltage across the terminals of the battery should be around 13.5V.

If the voltage of a battery is less than 12.7V while the engine is running, you should replace the alternator.

Before replacing the alternator, also check if the serpentine belt connected to the pulley of the alternator is damaged or not. If the serpentine belt is loose, it will not run the alternator properly.

6. Bad Starter

A bad starter can also cause the car not to start. You replaced the battery because the car was not starting.

But the chances are that the car starter has gone bad. A starter has a solenoid that energizes when an electric current is passed through it from the battery via the ignition switch.

The solenoid of the starter is an electromagnet because it requires a very small current to energize.

When current passes through the coil, the magnetic field moves the plunger inside the starter that closes the electrical copper contacts and completes the circuit to rotate the starter motor.

The electrical contacts relay a proportionately larger electrical current through themselves and to the starter motor. 

If the dash lights are on but your car is not starting, the chances are that the starter motor or ignition switch has gone bad.

Must Read: Car makes whirring noise but won’t start

How to diagnose?

Before replacing the starter, make sure that the wire from the positive terminal of the battery to the starter is installed properly.

The starter receives two wires from the positive terminal of the battery. One is a small wire that carries only a small amount of current to power the solenoid.

This small wire passes through the ignition switch. The other is a large wire connected directly with the positive terminal of the battery. Make sure that you have properly connected these two wires to the starter.

If the connections are fine, try to tap the starter repeatedly with a big wrench and see if the car starts or not.

Sometimes, the plunger inside the solenoid of the starter gets stuck. So, tapping a starter with a heavy hammer can help in driving the starter motor.

7. Seized Engine

During normal operation, an engine’s pistons slide up and down smoothly inside the cylinders. The connecting rods translate the reciprocating motion of the pistons to the rotating crankshaft.

For this to happen, a thin film of oil coats the cylinder walls, rings, bearings, and other internal components. This oil film prevents metal-to-metal contact and friction while also dissipating heat.

When an engine seizes, the lack of lubrication causes metal surfaces to weld together through excessive friction and heat. The pistons can no longer move freely in the cylinders.

Connecting rods may bend or break under the stress. Bearings may overheat and melt. The crankshaft itself can become stuck in place, unable to rotate. This damage makes it impossible for the starter motor to crank the engine to begin the combustion process.

How to test?

To test a seized engine, put a big wrench on a crankshaft pulley and try to rotate it. If it doesn’t rotate freely, it means the engine has seized.

8. Bad Fuel Pump

A bad fuel pump may also prevent your car from starting if it fails to pump a certain amount of fuel out of the tank.

Open the gas cap door. Try listening for the fuel pump as someone turns on ignition.

When the key hits on, the pump runs briefly, building pressure. The whirring sound of the pump inside the tank is audible if you take off the cap.

If no sound, first check the fuse and wiring of the pump.

Bonus Read: Common problems after changing fuel pump

9. Bad Fuel Injectors

If your car has been sitting idle for a longer time, the chances are that fuel injectors become clogged and are not injecting the fuel.

So, you also have to check if the fuel injectors are injecting the fuel properly. You can check my guide on car won’t start after replacing the fuel injector. I have discussed the whole procedure there.

10. Damaged Key Fob

In cars like Mercedes, a damaged key fob can also cause the car not to start when you try to replace the car battery.

There are chances that you tried to jump-start the battery to start the car when the key was in the ignition.

This might have ruined the communication module of the key. In such a case, you will have to get a new key fob.

Final Thoughts About Car Not Starting After Changing Battery

In summary, car not starting after replacing battery can be a frustrating and costly issue that can have various causes and solutions.

Some of the common causes are loose or corroded battery terminals, damaged battery, faulty starter, seized engine, bad fuel pump, bad fuel injectors, or damaged key fob.

Some of the common solutions are checking the battery terminals, replacing the battery, testing the starter, inspecting the engine, and cleaning the fuel system. However, if the problem persists or worsens, it is advisable to consult a mechanic for professional help.

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