Car Battery replacement & repair made easy

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.