Quick answer
Switch everything off, disconnect the negative (−) terminal first, then the positive (+), undo the hold-down and lift the old battery out. Fit a battery of the same size, type and rating, secure it, then connect positive first and negative last. If your car has stop-start it needs an EFB or AGM battery, and some cars also need the new battery registered with a scan tool.
Is this a DIY job?
- Difficulty: Easy on most cars; Medium if the battery is under a seat, in the boot or needs registration
- Time: 20 to 45 minutes
- Tools: spanners or sockets (often 10 mm, but check), terminal brush, safety glasses, gloves
- Skills: basic hand tools and careful lifting
On most cars with the battery under the bonnet, this is a straightforward DIY job. Check two things before you start: whether your car needs battery registration (see step 2), and what type of battery it uses (see the specs table).
Step by step
- Get the right battery. Read the label on your old battery or check the owner’s manual. Match the physical size, terminal layout (which side the positive post is on), type and cold cranking amps (CCA). Never fit a lower type than the original: a stop-start car that came with an AGM battery needs an AGM replacement.
- Check your manual for extras. Some cars need the new battery registered (coded) to the battery management system with a scan tool. If that’s skipped, stop-start and charging may not work properly. Also check whether you’ll need a radio code and how to reset power windows after the battery has been disconnected.
- Gear up and make it safe. Wear safety glasses and gloves. Take off rings and metal watch bands. Park on level ground, switch off the ignition and all accessories, and take the key out. No smoking or flames: batteries can give off hydrogen gas.
- Disconnect the negative (−) terminal first. It’s usually black and marked “−” or “NEG”. Loosen the clamp nut, twist the clamp off the post and tuck it away so it can’t spring back and touch the post.
- Disconnect the positive (+) terminal. It’s usually red, often under a plastic cover. Loosen it and lift it off. Don’t let your spanner touch any metal part of the car while it’s on the positive terminal.
- Remove the hold-down. Undo the clamp, bar or bracket that holds the battery in place. If there’s a small vent tube on the side of the battery (common on batteries in the boot or cabin), unclip it.
- Lift out the old battery. Batteries are heavy. Keep it upright, use the handle if it has one, and lift with your legs. Put it somewhere it can’t tip over.
- Clean up. Brush any corrosion off the terminal clamps and the tray. Check the cables for cracks, swelling or green corrosion under the insulation. Replace damaged cables before fitting the new battery.
- Fit the new battery. Sit it in the tray the same way round as the old one, so the positive post lines up with the positive cable. Refit the vent tube if there is one.
- Secure the hold-down. The battery must not move when you push it. A loose battery can short out or crack under vibration.
- Connect the positive (+) terminal first. Push the clamp fully down on the post and tighten it firmly. Don’t over-tighten: lead posts are soft. Refit the red cover.
- Connect the negative (−) terminal last. Tighten it the same way. A small spark as it touches is normal. Spray both terminals with terminal protector.
- Start and check. Start the car and check that no warning lights stay on. Reset the clock, radio presets and window auto-up if needed. Some cars idle a little oddly for the first few minutes while the engine computer relearns.
- Register the battery if your car needs it. If your manual or the battery supplier says registration is required, have it done with a suitable scan tool.
- Recycle the old battery. Don’t put it in a household bin. Battery retailers, many workshops, scrap metal dealers and council drop-off points accept lead-acid batteries.
Using a memory saver
A memory saver plugs into the OBD port or 12V socket and keeps a little power on so you don’t lose radio and settings. If you use one, remember the battery cables are still live. Keep the positive clamp wrapped or covered so it can’t touch the body. If you’re not confident, it’s safer to skip the memory saver and reset things afterwards.
Specs table
Which battery type?
| Type | What it is | Typically fitted to |
|---|---|---|
| Conventional flooded (wet cell) | Standard lead-acid with liquid electrolyte | Older cars and many cars without stop-start |
| EFB (Enhanced Flooded Battery) | Flooded battery built to handle more frequent starts | Many entry-level stop-start cars |
| AGM (Absorbent Glass Mat) | Electrolyte held in glass mats; sealed and spill-resistant | Stop-start cars with brake energy recovery, high-demand vehicles, batteries in cabin or boot |
| Lithium (12V) | Lithium starting battery | Some hybrids, EVs and performance vehicles: only where the maker specifies |
Rule of thumb: replace like for like. Don’t fit a conventional battery where an EFB or AGM was fitted at the factory, and always replace AGM with AGM. If you upgrade from EFB to AGM, the car may need the new battery type set in its system.
Terminal order
| Job | First | Last |
|---|---|---|
| Removing | Negative (−) | Positive (+) |
| Fitting | Positive (+) | Negative (−) |
Why: once the negative is off, touching the car’s body with a spanner on the positive terminal can’t cause a short.
What you’ll need
- car battery (matched to your vehicle; AGM car battery or EFB car battery for stop-start)
- battery terminal brush
- battery terminal protector spray
- battery terminal clamp (if the old ones are damaged)
- memory saver (optional)
- safety glasses and nitrile gloves
When to call an auto electrician
- Your car needs battery registration or coding and you don’t have a suitable scan tool.
- The battery is hard to get to (under a seat, behind a wheel arch liner, under the floor).
- The cables or terminals are badly corroded, melted or cracked.
- The new battery goes flat again within days or weeks. That points to a charging fault or a parasitic drain.
- Warning lights stay on after the battery change.
- It’s a hybrid or EV. You can often replace the 12V battery yourself if the manual allows it, but never touch the high-voltage battery or any orange cables. Many hybrid 12V batteries are AGM and are often in the boot or under a seat with a vent tube.
Need an auto electrician? Find local auto electricians and mobile services in your city.
Related questions
Q: Can I fit a normal battery in a car with stop-start? A: No. Stop-start puts far more starts and deep cycles on the battery. A conventional battery will wear out quickly and the stop-start system may stop working. Fit EFB or AGM, matching what the factory fitted. (see What’s the difference between flooded, EFB, AGM and lithium car batteries?)
Q: Why do you take the negative terminal off first? A: The car’s body is connected to the negative terminal. If you undo the positive first and your spanner touches the body, you create a direct short. Taking the negative off first removes that risk.
Q: What is battery registration? A: On some cars, the battery management system needs to be told a new battery has been fitted so it can adjust charging. It’s done with a scan tool. Skipping it can affect stop-start and shorten the new battery’s life.
Q: How do I know what size battery my car needs? A: Check the label on the old battery, the owner’s manual or a battery fitment guide for your make and model. Match the size, terminal layout, type and CCA.
Q: Will I lose my radio and settings? A: You may lose radio presets, the clock and window auto-up settings. Some older radios need a security code, which is usually in the owner’s manual or service book.
Sources
- RACV, “Car battery replacement” – some vehicles have a battery management system that requires new batteries to be registered. https://racv.com.au/on-the-road/roadside-assistance/car-battery-replacement.html (checked October 2026)
- VARTA, “The right code of the BEM for battery replacement” – which makes need active registration and the effect on stop-start if skipped. https://www.varta-automotive.com/en/knowledge/articles/article-details/the-right-code-of-the-bem-for-battery-replacement (checked October 2026)
- Banner Batteries, “How-to: registering start-stop batteries” – open and closed systems; effects of not registering on some makes; AGM must be replaced with AGM; an EFB-to-AGM upgrade must be configured; never replace EFB or AGM with a conventional battery. https://www.bannerbatterien.com/en/Battery-knowledge/7-HOW-TO-Registering-the-battery (checked October 2026)
- VARTA, “AGM technology” – AGM for start-stop with regenerative braking, high electrical demand and hybrids; EFB for entry-level start-stop. https://www.varta-automotive.com/en-gb/knowledge/technology/agm (checked October 2026)
- Planet Ark, Recycling Near You, “Recycling lead-acid batteries” – don’t put in bins; where to take them; about 97% of materials recyclable. https://recyclingnearyou.com.au/car-batteries (checked October 2026)