How to Replace the Battery on a Mercedes-Benz | C-class W203 W209
Are you having a hard time getting your Mercedes-Benz C/CLK-Class to start? Your battery might be dead. Learn how to fix the problem by replacing the battery of your Mercedes-Benz C or CLK-Class.
NOTE: This guide shows you how to change the battery in a Mercedes CLK-Class and a W203 C-Class. The battery is located in the same place in both of these vehicles, so the procedure is identical. Are you more of a visual learner? Follow along with our video guide below:
What you will need
- AGM-94 Battery
- Group Size H8
- Minimum Cold Cranking Amps 760
- Flathead Screwdriver
- 3/8 Ratchet
- 3/8 Long Extension
- 3/8 Long 10mm Socket
- 3/8 Long 13mm Socket
- A flashlight or a Reliable Light Source
- Extendable Magnet
Procedure
- Gather your tools and ensure the new battery is fully charged.
- Park the vehicle on flat ground with a reliable light source and engage the parking brakes.
- Turn the ignition to the off position, and remove the key from the ignition.
- Open the hood by pulling the hood release latch located below the steering wheel. Before you begin, make sure the hood will stay open. Sometimes, the hood struts weaken, causing the hood to close as you work. Have a friend help keep the hood open if the hood doesn’t stay up.
- Using a flathead screwdriver, carefully pop open the three clips holding the battery cover in place.
- Remove the cover and set it aside.
- To properly unground the battery, loosen the negative (-) battery terminal nut with a 10mm socket, then move the terminal.
- Loosen the positive (+) battery terminal nut with a 10mm socket and move the terminal wire to the side.
- Using the 13mm socket, remove the two nuts keeping the battery in place. There is one on each side of the battery. Space is tight, so a pickup magnet can help in this step. Remove the mounting bracket and move all the cables out of the way.
- Disconnect the vent hose from the bottom of the battery. If your car has an AGM battery, it will not have a vent hose.
- The battery can now be removed and lifted by the two handles. Careful, these batteries are heavy! Get someone to help you lift the old battery.
- Insert the new battery carefully into the vehicle, remembering that the Negative Terminal is on the left and the Positive Terminal is on the right.
- Reconnect the vent hose and ensure the mounting bracket is lined up.
- Insert each 13mm nut back into the mounting points on each side and tighten them to specification.
- Use a terminal wire brush to clean the terminals when possible.
- Connect the positive (+) cable back onto the positive battery terminal and tighten it with the 10mm nut.
- Repeat the same steps for the negative cable.
- Place the battery cover back on top of the battery and lock in the three tabs.
We do not recommend using a backup battery to keep the vehicle powered up while you replace the battery. While connecting a backup battery saves a few minutes, it introduces unnecessary risk, especially if there is an accidental short or insufficient power to keep all vehicle systems powered up.
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Torque Specifications
- 10 ft/lbs. for both terminals
- 25 ft/lbs. for each mounting bracket bolt
Tips & Tricks
- The Positive terminal is always on the right if looking at the car from the front.
- The Negative terminal is always on the left, looking at the car from the front.
- Always check the size, AMPs, and volts of the new battery compared to the old battery.
- After disconnecting the terminals, use a wire brush to carefully clean them and ensure there is no significant corrosion.
- Do not leave the key in the ignition while you replace your Mercedes-Benz C CLK battery. This can cause problems with the EIS module, and the vehicle may not start.
- Once the vehicle starts, ESP and ABS lights may come on. This is due to the steering angle sensor needing calibration. To reset the steering angle sensor, start the engine and turn the steering wheel to the left and right several times.
- Synchronize the sunroof and windows by pressing the button and keeping it pressed for five seconds after the window/sunroof reaches fully open and closed positions.
Resetting Fault Codes
When fault codes appear after you replace your battery, you can reset it with an OBD-II scanner, such as the YOUCANIC Full System Scanner. This powerful device can read and clear codes from all the systems in your Mercedes-Benz.
We hope you find the Mercedes-Benz C / CLK Battery Replacement Guide / W203 W209 guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.
