How to Replace a Car Battery: Step by Step, and When Not to Do It Yourself

Quick answer

Before you start: is this a job for you?

Replacing a battery on an older car with the battery under the bonnet is a manageable DIY job. Think twice if any of these apply:

• Your car has start-stop or an AGM battery. Many BMW, Mini, Audi, Volkswagen, Land Rover, Jaguar and Jeep models expect the new battery to be registered with a diagnostic tool. Skip it and the car may charge the new battery as if it were the old one. See AGM and EFB batteries.
• The battery is in the boot, under a seat or under the floor. Common on European cars. Access is awkward, and some have vent tubes that must be refitted.
• It is summer and the engine is hot. In UAE heat the engine bay and metal parts can burn you. Let the car cool, and work in shade.
• You don't have the radio or security codes. Some cars lose radio codes, window and sunroof positions or seat memory when the battery is disconnected.

Tools you need

• Spanners or a socket set (10 mm fits most terminals; hold-downs vary)
• Safety glasses and gloves
• A terminal brush or wire brush, and a cloth
• A memory saver, if you want to keep your settings (optional)
• The correct replacement battery

Match the new battery

Check four things against the old battery's label:

1. Physical size, so it sits in the tray and the hold-down fits.
2. Terminal layout (L or R in JIS codes). Positive and negative must be on the same sides as before, or the cables won't reach.
3. Capacity (Ah) and cold cranking amps (CCA). Match them or go slightly higher. Our guide to car battery sizes decodes labels like 55D23L.
4. Type: conventional, EFB or AGM. Replace AGM with AGM.

Step by step

1. Park safely and switch everything off. Engine off, key out (or keyless fob away from the car), lights and accessories off.
2. Connect a memory saver if you are using one, following its instructions.
3. Disconnect the negative (−) terminal first. Loosen the clamp and move the cable away so it can't spring back onto the post. Taking the negative off first means a spanner that touches the bodywork while you work on the positive won't cause a short.
4. Disconnect the positive (+) terminal. Lift the red cover if there is one.
5. Remove the hold-down clamp or bracket.
6. Lift the old battery out. Keep it upright: a car battery is heavy and contains acid. Lift with your legs, not your back.
7. Clean the tray and terminal clamps. White or green crust is corrosion. Brush it off, wearing gloves.
8. Fit the new battery the same way round as the old one, and refit any vent tube.
9. Secure the hold-down. A loose battery vibrates, which shortens its life and can damage the case.
10. Connect the positive (+) first, then the negative (−). Tighten the clamps firmly so they don't twist on the posts, but don't over-tighten.
11. Start the car and check the warning lights clear.

How long does it take?

Battery location	Doing it yourself	Mobile technician
Under the bonnet, easy access	About 30 to 60 minutes the first time	Usually a quick swap once the battery is confirmed
In the boot or under the floor	An hour or more	Longer than an under-bonnet swap
Under a seat, or needing registration	Not recommended without the right tools	Confirmed before booking

What to check afterwards

• Charging voltage. With the engine running, a multimeter across the battery should usually read about 13.7 to 14.7 V on most cars. Close to the engine-off reading means the alternator may not be charging. Smart alternators vary this deliberately, so treat it as one clue.
• Settings. Reset the clock and radio. Some cars need the windows or sunroof re-taught: usually run the window fully down and up, holding the switch for a few seconds. Check your owner's manual.
• Warning lights. A start-stop or battery message that stays on can mean the battery needs registering.

Disposing of the old battery

Car batteries contain lead and sulphuric acid. In the UAE they must go to licensed collectors, never general waste. Battery shops and service centres usually take old batteries back when you buy a new one. When we replace a battery, we take the old one away for recycling.

Prefer not to do it yourself?

Our technicians come to your car at home, at work or at the roadside in Dubai, Abu Dhabi and Sharjah. We test the old battery first, confirm the right replacement and the full fitted price, fit it and take the old one away. See how mobile battery replacement works and fitted prices.

Sources

• Varta: Correct battery care
• Varta: Testing the battery step by step
• Interstate Batteries: FAQs