These instructions apply to the Mercedes C-Class Mk3 (W204) 2007-2014.
For other models, please choose your vehicle here.
Short answer: to disconnect the 12V battery on the Mercedes C-Class W204 (2007–2014) safely, switch everything off and wait a couple of minutes, then undo the negative (−) terminal first. On reconnecting, fit the positive (+) first and the negative last, switch the ignition on and wait a minute before starting.
Before You Disconnect
The main 12V battery is under the bonnet. Never undo the terminals with the engine running. Disconnecting the battery will clear the clock, and the windows, sunroof and tyre-pressure system usually need re-initialising afterwards — so plan to run those resets once it’s back on.
Disconnect the Battery
- Switch the ignition off, remove the key and close the doors; wait about two minutes for the systems to power down.
- Undo the negative (−) terminal first.
- Undo the positive (+) only if you need to remove the battery.
Reconnect the Battery
- Fit the positive (+) first, then the negative (−), and make sure both clamps are clean and tight.
- Switch the ignition on and wait about a minute before starting, so the electronics re-initialise.
- Restore the settings that cleared: re-initialise the electric windows and the sunroof, reset the tyre-pressure system, and set the clock.
If a warning stays on after this, have it read by a specialist.
Notes
- The W204 uses a maintenance-free battery; if you’re replacing it, fit the correct type and rating for the car.
- Some models also have a small backup battery for the safety systems — a persistent warning after a battery change should be diagnosed rather than ignored.
Frequently Asked Questions
Which battery terminal do I remove first on a W204?
The negative (−) first. On reconnection, fit the positive (+) first and the negative last.
What needs resetting after disconnecting the W204 battery?
The clock, the one-touch windows and sunroof (re-normalise them), and the tyre-pressure system. The radio does not normally need a code on the W204.
How long should I wait before disconnecting?
Switch off, remove the key, close the doors and wait about two minutes so the control units power down before you undo the terminals.
Why won’t my windows work after reconnecting the battery?
They lost their learned end stops. Re-normalise each one (hold up to close and hold, down to open, up to close) — see our W204 window re-initialisation guide.
If a warning light remained on after reconnecting, look it up on our sister site autodtcs.com to see whether it points to a fault.
Independent guide — not affiliated with Mercedes. Always follow your official service manual and safety precautions. Read our full disclaimer.