Tools Needed
- 10mm and 13mm spanners or sockets
- Wire brush or battery terminal cleaner
- Petroleum jelly or terminal protector spray
- Memory saver (optional but recommended)
Step-by-Step
- Turn off the ignition and remove the key.
- Connect a memory saver if you have one (preserves radio code and settings).
- Disconnect the negative (-) terminal first using a 10mm spanner.
- Disconnect the positive (+) terminal.
- Remove the battery hold-down clamp (usually 13mm).
- Lift the old battery out — they’re heavy (15-25kg).
- Clean the terminals and battery tray with a wire brush.
- Place the new battery in the tray and secure the clamp.
- Connect the positive (+) terminal first.
- Connect the negative (-) terminal last.
- Apply petroleum jelly to both terminals to prevent corrosion.
Start-Stop Battery Registration
If your car has start-stop, the battery management system (BMS) needs to know a new battery has been fitted. Without registration, the BMS still thinks the old battery is fitted and won’t charge the new one correctly, leading to premature failure.
Start-stop vehicles: After fitting a new battery, you need a diagnostic tool to register it with the BMS. This typically costs £20-30 at a garage with the correct software. BMW, Mercedes, VW/Audi, and Volvo all require this step.
Frequently Asked Questions
Is replacing a car battery dangerous?
Low risk if you follow the correct order: negative off first, positive on first. The main dangers are shorting the terminals (sparks) and the weight of the battery. Always remove jewellery and wear gloves.
Will I lose my radio code?
Possibly — disconnecting the battery resets volatile memory. Use a memory saver or have your radio code ready. It’s usually on a card in your handbook.
How often should I replace my car battery?
Every 4-6 years on average. Start-stop vehicles may need more frequent replacement (3-5 years) due to the higher cycling demands.
