Signs Of A Bad Car Battery

8 Signs Of A Bad Car Battery

Here is a short list of the most common signs of a bad car battery:-

  • Car struggles when starting.
  • Car fails to start with a weak or no ignition sound.
  • Car fails to start, and a clicking sound can be heard.
  • Headlights are very dim when the car engine is off.
  • Central locking fails to work.
  • Electrical powered windows, seats, and windshield wipers are weak when the car engine is off.
  • Damage to the car battery casing.
  • Strange eggy smell coming from the car battery.

In this article, I have researched some of the most common signs that are reported from a weak or failing car battery.

I will also help you to learn some of the false flags to look out for when making your diagnosis.  Electrical issues can be complex at times, and a healthy battery can appear worn out when the problem is elsewhere, so never jump to conclusions.

Engine Struggles To Start

One common sign of a bad car battery is when your car engine struggles to start.

A failing car battery may provide a weak start or even no start at all, but still have enough energy to power everything else as it should.

You may also find that your car struggles to start but runs fine once started.

The alternator supplies most of the energy throughout the electrical system once you have started your car.  To get your car started, the battery itself powers the starter motor so that it can crank the engine.

The starter motor requires quite a lot of power to crank the engine.  A weak or worn out battery will cause the engine of your car to crank much slower than usual, or it may begin to crank and then stop altogether.

Rapid Clicking When Trying To Start Car

If your battery is too weak to crank the engine, you may only hear a rapid clicking when trying to start your car.

A basic starter motor on a petrol car has an arm that pushes out to engage with the gears of the cranking mechanism before actually cranking the engine.

The diagram below shows an exploded view of a vehicles starter motor assembly.  You can see the solenoid and switch at one end of the starter motor and at the other end you can see the gear which pushes out to engage with the cranking mechanism.

Faulty Starter Motor Diagram
Starter Motor Diagram

The rapid clicking is the sound of the solenoid opening and closing rapidly (which requires very little power), but failing to engage or crank the engine.

Although the rapid clicking sound is a common sign of a bad car battery, this may also signal a faulty starter motor.  These are the types of false flags you should look out for, and you will need to check for further signs of battery issues before assuming you have a bad battery.

Engine Won’t Turn Over At All

If your engine won’t turn over at all, your battery may be completely dead. It should be easy to diagnose a battery that is totally flat by checking if anything else in the car is receiving power. Headlights and windshield wipers are a good indicator.

If there does appear to be power, but the engine will not crank, you may have an immobilizer issue or a dead starter motor. More false flags to be aware of.

My Car Battery Smells Like Rotten Eggs

There are a few reasons why you may smell a rotten egg type of odor around your car, and if you are sure that the smell is coming from your car battery, then it may be faulty or leaking.

Lead-acid car batteries contain sulphuric acid. If your car battery is leaking, the escaping sulfur can smell like rotten eggs. Not only can the leaking acid cause damage to your car components and electronics, the battery also requires this acid to function correctly.

If you do experience a rotten egg type of smell, have positively identified a leak to your car battery, and have found the source of the leak to be from damage to your battery, it will need replacing. Damage to look for will be swelling or cracks to the battery casing.

Most car batteries are sealed and maintenance-free so are unlikely to leak unless there is some form of damage. If there is no clear sign of damage, and you are sure that your battery is leaking, you could attempt to refill the battery.

There are many useful guides on the internet on how to refill your battery. Check out the video below from Supercar Central.

FALSE FLAG ALERT! If there are no obvious leaks from your battery, there may be other reasons for the rotten egg smell.

Assuming that you have not left your egg sandwiches from last week in your glove box, below are two other reasons why you may experience a smell of rotten eggs, and are not caused by a bad battery

Batteries that have been charging without adequate ventilation can give off sulfur which can smell like rotten eggs.

Catalytic converters can give off a rotten egg type of smell when hot.

As I have mentioned previously, if you are unsure if your battery is faulty, always check for several indicators before making a diagnosis.

Car Battery Is Not Holding Its Charge

Another sign of a failing battery is when it stops holding its charge.  If your car has been sitting for a short while, you may find some of the electrical systems will either fail to work or appear weak.

There are several electrical issues that you may find when your battery is not holding its charge.  Some examples are below:

  • Your central locking may be slow to work or may fail completely.
  • Electric windows may be slow or not work at all.
  • Your car alarm may not work.
  • Headlights may be very weak and brighten when revving the engine.
  • Windshield wipers will be very slow.
  • Horn sounds weak.

These are just some of the electrical issues that you may experience if you have a bad or discharged battery.

Although not advised, a healthy battery should be able to power a cars headlights and radio for several hours with the ignition switched off before running flat.

A healthy car battery should hold its charge for several weeks without use, provided you have previously taken your car on regular trips that are at least 20-30 minutes long.

If you are experiencing any of the above issues, it will be doubtful that your car will start.  If this is the case, you will need to jump start your car.

You can find more information on jump starting by reading our How To Jump Start A Car Manually guide, our How To Jump Start A Car With Jumper Cables guide, or our How To Jump Start A Car With A Portable Jump Starter guide. 

There are several reasons why a battery may not hold its charge, and battery age is a critical factor.

As a car battery ages, it’s fluid or electrolyte levels may decrease.  There could be sulfation of the lead plates inside of the battery or corrosion to the battery terminals.

Corroded battery terminals would stop the battery from receiving a healthy level of charge, and simply brushing with a wire brush can solve this particular issue.

You should note that a frequently discharging battery may still be healthy, and you may have a faulty or failing alternator.

An alternator should provide a charge to the battery when the car engine is running.  A worn-out alternator may only provide enough energy to power the cars electrical system.

Worn out alternator belts are a common problem and are easy to replace at a very low cost.  Many people are capable of replacing these belts by themselves.

The brushes inside of an alternator also suffer from wear over time and will cause the alternator to generate far less energy than it should.

An illuminated battery symbol on your dashboard, similar to the image below, will usually point to a faulty alternator. 

car battery warning light

The battery symbol will stay illuminated even after the car has started.

Alternators are pretty cheap to replace, and you can pick up a reconditioned one for much less than a new one if you shop around.

My Car Battery Drains Overnight

One other issue that is quite common, especially on older vehicles, is faulty wiring or a bad earth connection.  These can cause your car battery to drain overnight or when not in use.

If you are experiencing this particular issue, you firstly need to check that nothing is left switched on when you leave your car, especially internal reading lamps.

Faulty wiring can cause a permanent drain on the battery, so even a brand new battery will continue to discharge when the car is not in use.  Finding a bad earth or wiring fault can be difficult at the best of times and can even be exaggerated when moisture is present as an added conductor.

It would be advisable to enlist the help of a qualified electrician who will need to use a testing tool such as a multimeter to trace all wiring from the battery.

It can be a very complicated task to find this type of battery drain, and sometimes, will go undiagnosed.

If the cause of your mysterious battery drain cannot be located, short of needing a complete rewire, you would need to disconnect your battery completely whenever it is not in use.  Alternatively, an isolation switch can be added, which will disconnect the battery by hand.


Hopefully, this guide has helped you to understand the most common signs to look for when diagnosing a bad car battery.

Never assume that your problems are because of a bad battery, and you should always look out for two or more symptoms before making your diagnosis.

A faulty car battery needs replacing as soon as possible as it will only get worse and cause you further problems with starting and operating your car.

If you struggle with the cost of buying new batteries, another option that many people are turning to is battery reconditioning.

You can recondition most types of battery by using the right techniques and methods, and battery reconditioning can often rejuvenate a battery back to 100% of its original health.

Assuming that a battery is suffering from one of the many typical and fixable issues, a battery can usually get reconditioned many times before being discarded. A damaged battery cannot be reconditioned.

I have reviewed the battery reconditioning system that I use, which is very effective and easy to use.  You can read my review of the EZ Battery Reconditioning System here, where you will also find the product link.

A short introductory video of the system can be found below.

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