How to change a car battery, step by step

To change a car battery, switch everything off, disconnect the negative (black, −) terminal first, then the positive (red, +), remove the hold-down and lift the battery out. Fit the new battery in the same position, connect the positive first and the negative last, then tighten the hold-down.

On many modern cars there are extra steps: the battery may be in the boot or under a seat, it may need to be AGM or EFB, and the car may need to be told a new battery has been fitted.

Can I change the battery myself?

It depends on the car. Check this table before you start.

Car type	DIY?	What to watch for
Older Japanese or Korean saloon, no start-stop (e.g. older Corolla, Sunny, Accent)	Yes	Match the size, terminal layout and capacity
Car with start-stop	Possible	Must be EFB or AGM, matching what was fitted. See AGM vs EFB vs conventional
European car with a battery management system (BMW, Mercedes-Benz, Audi, VW, Porsche, Land Rover)	Battery swap yes, but registration needed	The new battery must be registered or coded with a diagnostic tool
Battery in the boot or under a seat	Possible	Vent tube must be refitted; access panels and trim to remove
Hybrid (12V auxiliary battery)	Check first	The 12V battery is often in the boot or under a rear seat, not under the bonnet. Never touch the high-voltage system (orange cables)
Large 4x4 or car with two batteries	Possible	Heavy batteries; check both and the isolator or link cables

The label on the fitted battery shows the technology, capacity (Ah), cold cranking amps (CCA) and size. Our car battery size chart explains the codes.

Tools you need

• 10mm and 13mm spanners or sockets. Most terminal clamps are 10mm. Hold-down clamps are often 10mm or 13mm, sometimes with an extension bar.
• Gloves and eye protection. Battery acid burns skin and eyes.
• A memory saver (optional). It plugs into the OBD port or the 12V socket and keeps radio presets, clock and some settings while the battery is out.
• A wire brush or terminal cleaner and a cloth.
• Petroleum jelly or terminal protection spray (optional).

Safety first: hydrogen gas and heat

Safety box

• Lead-acid batteries can give off hydrogen gas, which is explosive. No smoking, no sparks and no flames near the battery.
• Do not let a metal tool touch the positive terminal and the car body at the same time. That is a direct short circuit and it can burn you or weld the tool.
• Remove rings, watches and metal bracelets.
• In summer, the battery and engine bay can be very hot. Let the engine cool before you work under the bonnet. Do not work on a battery that is swollen, leaking or smells of rotten eggs. Read what a smelling, leaking or swollen battery means.
• A battery is heavy. Lift with your legs and keep it upright so acid cannot spill.

Step by step

1. Prepare the car

Park on level ground, apply the handbrake and switch off the ignition and all electrical loads. Keep a smart key away from the car. Write down the radio code if your car uses one, and connect the memory saver if you have one.

2. Find the battery and note its position

Take a photo of how the battery sits and which side the positive terminal is on. The new battery must fit the same way round.

3. Disconnect the negative terminal first

Loosen the clamp on the negative (−, usually black) terminal and lift it off. Move the cable away so it cannot spring back onto the post.

The negative goes first because it is connected to the car body. Once it is off, touching the body with your spanner while working on the positive terminal will not cause a short. Our guide to which battery terminal to disconnect first explains this in more detail.

4. Disconnect the positive terminal

Lift the plastic cover, loosen the clamp on the positive (+, usually red) terminal and remove it.

5. Remove the hold-down and vent tube

Every battery is held in place by a clamp at the base, a bar across the top or a bracket. Remove it and keep the bolts safe.

Batteries fitted in the boot or cabin usually have a vent tube that carries gas outside the car. Unclip it carefully.

6. Lift out the old battery

Lift it straight up, keeping it level, and put it where it cannot tip over.

7. Clean the tray and terminals

Check the battery tray for acid, corrosion or debris. Clean the cable clamps with a wire brush until the metal is bright. White or green deposits can stop a new battery working properly.

8. Check the new battery

Before fitting, check:

• Technology, size and capacity match the old battery or the car’s specification.
• Terminal layout matches. A battery with the terminals the wrong way round will not fit the cables.
• Date code. Batteries lose charge on the shelf, faster in heat. Look for the manufacture date on the label or case. The format varies by brand; if you cannot read it, ask the seller. Avoid batteries that have been in stock for a long time.
• Voltage, if you have a multimeter. A new, fully charged battery should read about 12.6V or more. See our car battery voltage chart.

9. Fit the new battery

Place it in the tray the same way round as the old one. Refit the vent tube if there is one, then the hold-down. The battery must not move. A loose battery vibrates and fails early.

10. Connect the positive terminal first, then the negative

Fit the positive clamp and tighten it firmly, but do not force it. Refit the plastic cover. Then fit the negative clamp last. A small spark when the negative touches is normal.

Check both clamps by trying to twist them by hand. They should not turn.

11. Start the car

Start the engine. Some warning lights may appear and clear after a short drive. If they stay on, the car may need a diagnostic check.

What happens after the swap

Disconnecting the battery cuts power to the car’s electronics. On many cars you will notice one or more of these:

• Idle relearn. The engine may idle roughly or unevenly at first while the engine computer relearns. This usually settles after some driving. Some cars have a specific relearn procedure in the owner’s manual.
• Window auto-up and auto-down. One-touch windows often stop working. The usual fix is to close each window fully and hold the switch up for a few seconds. Check your owner’s manual for the exact steps.
• Radio code. Some cars, mostly older European models, ask for a security code before the radio will work again.
• Clock, presets, seat memory or sunroof may need resetting.
• Battery registration. On cars with a battery management system, the car must be told a new battery is fitted. Otherwise it charges the new battery as if it were the old, worn one, which can shorten its life and cause start-stop faults. This needs a diagnostic tool. See battery registration explained.

How to dispose of the old battery in the UAE

Lead-acid car batteries are hazardous waste. They contain lead and sulphuric acid and must not go in household bins or general waste.

Take the old battery to a battery seller, a workshop or an authorised recycler. Many sellers take the old battery when you buy a new one. Keep it upright and away from children until then.

When to call someone instead

Consider a professional fit if:

• your car needs battery registration or coding
• the battery is in the boot, under a seat or behind trim panels
• you are not sure the battery is the problem
• the car is a hybrid

We are a mobile service with no storefront. We come to your home, office or car park in Dubai, test the battery and charging system before replacing anything, fit the correct AGM, EFB or conventional battery for your car, register it where needed, and take the old battery away for recycling. Book car battery installation if you would rather not do it yourself.