How does a car battery work?
The vehicle's battery is the power storage unit for starting its engine. It’s location, be it under the bonnet, under the seats or in the boot is vital to the vehicle's operation and without its successful recharging once the engine is running, will leave you unable to restart the engine after the next time it’s stopped.
These days, with more and more cars and vans being equipped with an automatic stop/start system to reduce emissions, having a battery that is in top condition is becoming even more important and also more expensive.
The majority of batteries used in cars and vans are 12v, which in essence means they comprise 6 cells with 2 plates per cell. One of the plates is made from lead and one from lead dioxide and are submerged in a sulphuric acid formula (known as electrolyte) which sets off a reaction on the lead dioxide plate and produces ions. These ions cause the lead plate to produce hydrogen and a lead sulphate.
The end result is a chemical reaction that produces electrons and these electrons generate electricity, which then comes out the positive terminal of the battery and flows round in a circuit back through the negative terminal. On the way round it can power a multitude of items, from the starter motor to the glove box light! By applying a current to the battery in the right voltage, the battery can then be recharged.
In traditional wet flooded batteries and the newer enhanced flooded batteries (EFB) the electrolyte is in liquid form. In AGM batteries, the electrolyte is in gel form or in an advanced glass matt - hence AGM.
Simply put, the car battery stores and releases energy to start the engine and power electrical systems, and it gets recharged by the alternator while you drive.
What does a car battery replacement job involve?
Here’s a simplified overview of the process of what happens during a car battery replacement:
- First, the mechanic ensures the car is parked on a level surface with the engine turned off. The parking brake is engaged for safety.
- The mechanic locates the car battery, which is typically found under the hood but can sometimes be located in the trunk or under a seat, depending on the vehicle.
- Next, the mechanic identifies the battery terminals, noting the positive (+) and negative (-) connections. The negative terminal is usually disconnected first to prevent any electrical shorts.
- The mechanic uses a wrench to loosen and remove the clamp or bolt holding the negative terminal. Once the negative terminal is disconnected, they repeat the process for the positive terminal.
- Any brackets or hold-down clamps securing the battery in place are then removed. These are essential for keeping the battery stable while driving.
- The old battery is carefully lifted out of its compartment, and the mechanic inspects the battery tray and surrounding area for any signs of corrosion or damage. If any corrosion is found, it is cleaned.
- The new battery is then positioned in the tray, ensuring it is correctly oriented with the positive and negative terminals in the right positions.
- The hold-down clamps or brackets are reinstalled to secure the new battery in place.
- The mechanic reconnects the battery terminals, starting with the positive terminal followed by the negative terminal. They ensure the connections are tight and free of corrosion.
- Once the new battery is installed and connected, the mechanic starts the car to check for proper operation. They verify that all electrical systems are functioning correctly and that there are no warning lights on the dashboard.
This job requires skill and knowledge of eletricals, which is why it’s best done by a professional mechanic.
How do I know whether I need a car battery repair or replacement?
As a general rule, if your battery is more than three to five years old, it might be time for a replacement. Car batteries typically have a lifespan of about three to five years, depending on usage and environmental factors.
There are a few other tell tale signs to look out for when determining whether you need to replace the battery:
- If your engine cranks slowly when you try to start the car, it could indicate that the battery is losing its charge. A weak battery often struggles to provide the necessary power to start the engine.
- If you notice dim headlights or interior lights, especially when the engine is off, it might mean the battery is weakening. The lights rely on the battery for power, and dim lights can be a sign that the battery is failing.
- If you see the battery warning light on your dashboard, it’s a clear indicator that there might be an issue with the battery or the charging system. This light typically comes on when the battery isn’t being charged properly.
- If your car's electrical accessories, such as the radio, power windows, or air conditioning, start to malfunction or work intermittently, it could be due to a failing battery. These accessories depend on a consistent power supply from the battery.
- If you frequently need to jump-start your car, it’s a strong sign that the battery is no longer holding a charge properly and needs replacement.
What does a car battery replacement cover?
Unless otherwise stated, a ClickMechanic quote for your battery to be replaced will cover;
* The cost of the battery
* Coming to you
* Fitting of the battery
* Coding of the battery to the vehicle's electrical system (if required)
* Entering the radio code if required and present
* Ensuring the electric windows close and open as they should
* Checking that that charging system is working appropriately
* Disposal of the old parts (unless you request to keep them)
* VAT (if applicable)
* 12 months parts and labour warranty
How do I know whether it’s an alternator or a battery issue?
Observe the dashboard warning lights; a battery-shaped warning light typically points to an alternator problem.
Next, check the car’s behaviour when starting: a clicking noise usually indicates a battery issue, while a car that starts but then stalls likely have an alternator problem. To further diagnose, perform a voltage test using a multimeter if you are confident using one. A fully charged battery should read around 12.6 volts with the engine off and between 13.7 to 14.7 volts when the engine is running; lower readings suggest an alternator fault.
Additionally, dimming headlights or electronic accessories that don't work properly when the engine is running often signal alternator issues. On the other hand, if your car needs frequent jump-starts or the battery is more than three years old, it’s likely a battery issue.
Using these observations and tests can help you determine the right repair or replacement needed. If you’re not sure, it’s recommended that you book a diagnostic test to determine the exact issue.
Should I book an alternator replacement and battery replacement at the same time?
The alternator and battery work together to power your vehicle's electrical systems. If one is failing, it can affect the other. For instance, a failing alternator can lead to a drained battery, and a weak battery can put extra strain on the alternator.
If the battery is still holding a charge well and isn’t too old, it can often be reused. However, if it’s weak or near the end of its lifespan, it should be replaced too. It can sometimes be challenging to diagnose whether the alternator or battery is the primary issue. Replacing both components can eliminate any uncertainty and provide a fresh start for your vehicle’s electrical system.
In general, it is highly recommended to replace the alternator and battery at the same time if you want to ensure optimal performance and avoid future issues. This way, the cost of labour will be lower since the mechanic is already working on the electrical system.
Can a car battery be replaced by a mobile mechanic?
Yes, a battery can be replaced by a mobile mechanic as it is a fairly straightforward job for them. Mobile mechanics are equipped with the necessary tools and expertise to perform an alternator replacement at your location, providing convenience and saving you time.
By booking with a mobile mechanic, you can avoid the hassle of towing your vehicle to a shop and enjoy the flexibility of having the repair done at your home or workplace. Mobile mechanics are often cheaper than going to a garage.
To know more about the cost of alternator replacement, you can use our alternator replacement price estimator tool here.
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Frequently asked questions about car battery replacement & repairs
Read our answers to questions about car battery replacement costs, symptoms and more.
What does a vehicle’s battery replacement involve?
- Mechanic will inspect the electrical system.
- If necessary the battery is replaced
- Mechanic makes sure the battery's cables have not corroded or damaged before putting them back.
- Mechanic tests the battery charging system to confirm it is working as it should be.
Can I replace car battery myself?
Unless you are a qualified mechanic with the required skills, training and equipment to do the job, we strongly recommend a car battery replacement is only carried out by a professional mechanic. ClickMechanic can help get you a vetted and local mechanic to carry out the work. Just enter your postcode and your car's registration number at the top of this page and select the work needed to get an instant fixed price up front.
What are the signs that your car needs a new battery?
- You may initially find that when you unlock the vehicle, the central locking doesn’t work.
- When you turn the key in the ignition, you have no lights on the dashboard.
- When you attempt to start the engine, you get a very slow turn over, nothing at all or just a rapid clicking.
How long will a battery replacement take?
A car battery replacement usually takes under 1 hour, but can take more time. Ultimately, the time that the job will take will depend on a number of factors, like your vehicle's make and model, year, as well as other factors. Select your car at the top of this page for information on job time and cost for your vehicle through ClickMechanic.
How often should you replace a car battery?
Every battery will eventually lose its ability to provide the power for your car and all its electrical parts need to keep working. The problem is that the warning signs might give you very little notice that your car’s battery is about to fail completely.
Battery problems are the most common cause of callouts to vehicle recovery services, accounting for 1 in 5 faults, according to one major motoring organisation.
However, a lot of issues can be caused by incorrect battery replacement sequences. These days it's not always as simple as undoing the old one and popping the new one in its place. Some vehicles require the new battery to be registered and coded to the vehicles computer system for example or windows to be reset etc.
How do you know if your car needs a new battery?
Every time a battery goes “flat”, it can damage the cells in the unit and whilst it may show 12v the actual power of the battery is reduced. Therefore if you are having to get assistance to start a vehicle due to the battery, then you should really consider changing it.
With the newer batteries having higher demands on them, the lifespan has reduced and these batteries may only last 3 years. If you are buying a second hand car for instance, that has an automatic stop/start system, it's worth taking into consideration the cost of buying a new battery and replacing the one installed if it hasn’t been recently done.
Can I still drive with a faulty battery?
If you suspect there is any issue with your battery or there are concerns about its age or condition, book an inspection with a professional mechanic immediate effect. Driving with a dying or faulty battery can leave you stranded.
How much does it cost to fix a dead car battery?
Fixing a dead car battery may require replacement of the battery. Average cost for the replacement is £130. Battery prices for vehicles with a stop/start system are usually a bit higher.
How much does it cost to service a battery?
You can't technically service a car battery, if it is faulty it is commonly replaced. Cost for a battery replacement will vary between between £100 and £300, if your vehicle has a stop/start system the price could be a little higher.
How do I find the right battery for my car?
Your vehicle's manual will have guidance on the correct battery needed for the car. If you are unsure which battery is required, check with a professional mechanic, they will be able to help to identify which battery is needed for the car. Our in-house mechanic team can help find the right battery for you.
Should I charge or replace car battery?
Whether you need to replace or charge the battery will depend on the condition of the battery. If the battery is faulty then charging it will not help. If you're unsure whether you can still try charge your battery or if you need a new battery book an inspection wih a professional mechanic, they can check and advise on next steps.
Is a faulty battery an MOT failure?
Yes, batteries are checked as part of an MOT and hence your car can fail on an issue with the battery that is considered a major issue. For example it might be flagged that your car battery is mounted insecurely or that the battery is leaking.
What is the purpose of a car battery?
A car battery is responsible for starting the car, as well as powering other electrical systems in the car. It provides power to the starter motor, ignition system, and other electrical systems such as the stereo.
My car is not starting, how do I know if it's a battery, alternator or starter motor issue?
If you notice that the engine starts but dies soon after, then the alternator probably isn't keeping the battery charged. When you start up the car and notice that the interior lights are slowly fading, it could also indicate an issue with the alternator.
If you try jump starting the car and it works, it could imply an issue with the battery. However, it is important to note that a dead battery can also be caused by a failing alternator.
To test the starter, put on the headlights, if they don't come on, then the battery is probably flat or dead and may need to be recharged or replaced. If the headlights do come on, then try starting the car. If it still won't start, then the starter motor may be the problem.
What should I do if my car battery dies?
If the battery is flat (for reasons such as leaving headlights on) then you can jump leads to jump start it. If the battery is dead, then you will need to replace the battery completely.
Before attempting to jump start your car, first check that the battery is not leaking any acid as it could be a safety hazard. You'll need another person with a car to help as the process of jump starting is a two person job.
- Find the positive and negative terminals on the battery and attach the jump leads.
- The positive terminal will usually be marked with a "+" sign, while the negative terminal will usually be marked with a "-" sign.
- Have the other person start their car and let it run for a few minutes which should help charge up your battery.
- Once your car starts, drive around for 30 mins or so to fully charge up the battery.
If jump starting doesn't work, the problem could be something else and you'll need to seek professional help from a mechanic or technician.
Will a bad alternator affect a new battery?
Yes, a bad alternator can damage a new battery if it does not provide a consistent charge, it can also shorten the battery's lifespan.
Do I need a new battery after replacing alternator?
No, you don't need to in all circumstances. However, it depends on the initial fault and if the battery was also affected by the issue that led to the alternator replacement. If the battery is old or more than 5 years, then it may be worth replacing the battery as well.
How long should I drive to charge the car battery?
30 minutes of driving should be an adequate time to charge the battery on most modern cars. However, this time can depend on a number of factors. For example, driving 30 minutes on a motorway may be enough to charge the battery while if you're driving around town, it may take 1-3 hours to charge it up.
What is the warranty on a car battery?
Most car batteries come with a warranty of 3-5 years, but this can differ based on the manufacturer and the individual warranty conditions.
Is a car battery under warranty?
Battery is considered a "wear and tear" component so it's not always the case that the manufacturer's warranty will apply. With some manufacturer's the battery will be covered for the first year, however, so the best thing to do is check with the dealership or manufacturer.
How long can a car battery last without driving?
Typically, a car battery can last for up to 2 to 4 weeks without charging. In the case of relatively new and well-maintained car batteries, they can even last 2 months without a charge.
How much does it cost to replace a car battery?
A car battery replacement generally costs between £100 and £300 with an average price of £130. Battery prices for vehicles with a stop/start system are typically higher. Ultimately, the cost of a battery replacement depends on the type of battery your car's manufacturer recommends for your car. Find out what you could save by having your battery replaced by ClickMechanic by selecting your car at the top of this page!
Check out the ClickMechanic price for a car battery replacement. See the averages for different makes below. We consolidate industry standard data with millions of data points to give you the most accurate price. These estimates may include Stop/start Battery, Battery and/or Stop/start Battery.
Name | Average Cost | |
---|---|---|
Audi | £205 | Get exact price |
BMW | £221 | Get exact price |
Citroen | £159 | Get exact price |
Ford | £147 | Get exact price |
Land Rover | £212 | Get exact price |
Mercedes-Benz | £215 | Get exact price |
Nissan | £152 | Get exact price |
Peugeot | £152 | Get exact price |
Renault | £156 | Get exact price |
Toyota | £195 | Get exact price |
Vauxhall | £154 | Get exact price |
Volkswagen | £166 | Get exact price |
Estimates on average repair costs, such as the above results for a car battery replacement, are based on ClickMechanic's quote data which combines multiple third-party sources. Actual costs may vary. We provide estimates on average repair costs for information only and accept no liability for any inaccuracies or errors. If you think an estimate is incorrect, please contact us to let us know.
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Mechanics that undertake car battery work
- Bettley's Autos LTD, Kidsgrove
- Blue Star Automotive, Manchester
- Brewster's Auto Repairs, Haywards Heath
- JTS Mobile Autos, Elstree
- MPH Autos, Hunmanby
- Matts Vehicle Services, York
- OPI MOTORSPORT, Southampton
- TBR, Burton Upon Trent
- True-Blue Car Repairs, Birmingham
- UK Midland Tyres, Birmingham
- Xtec Autos, Abercynon
Turned up on time, had parts and tools needed, fixed my car quickly.”