Buzz
Is your Mercedes slow to crank on startup or failing to start altogether? The culprit could be the 'systems battery,' responsible for powering the entire car.
Step-by-Step Guide
Locate and inspect the battery. In many Mercedes-Benz models, you'll find the battery located under the hood, in the trunk, under the rear seat (W210), or under the front passenger seat (W164/166/151). On the G-wagen (W461/463), it's tucked under a cover in the floorboard behind the center console. Look for a sticker under the hood indicating 'battery in trunk' for vehicles with trunk-mounted batteries.
- For vehicles equipped with two batteries, the systems battery will be in the trunk, while the starter battery will be under the hood. If you're experiencing starting issues, focus on replacing the hood-mounted battery, typically a smaller white battery.
Use a DVOM (voltmeter) to check voltage. Take voltage readings by connecting the DVOM's test wires to the positive and negative terminals.
- An optimal battery will show a reading of 12.1-12.9 volts when the vehicle is off. Mercedes-Benz vehicles require a minimum of 11.4 volts to ensure proper operation of the onboard control units.
Get a Replacement Battery. Once you've assessed the battery's condition and acquired a replacement, double-check the amp hours (Ah) and cold cranking amps (CCA) on the battery sticker to ensure it matches your vehicle's specifications. Note that part numbers on the sticker may vary if the original battery is older.
Remove the Old Battery.
- For vehicles with exposed batteries under the hood, use a 10mm wrench or socket to detach battery cables and top mounts. Use a 13mm socket and extension to remove bottom mounts. You may also need to remove the cabin air filter box by releasing the snap clips on top and lifting it straight up.
- For vehicles with trunk-mounted batteries, lift the trunk floor panel to access the battery. On some models, loosen the strap around the battery by locating the buckle, usually on the side.
- For vehicles with two batteries, disconnect the negative cable from the starter battery before replacing the systems battery in the trunk.
Install the New Battery. Secure the new battery in place and connect the positive cable first, followed by the negative cable. Ensure proper fitting and bracketing to prevent shifting during driving.
- Always connect the negative cable last to avoid potential electrical arcing.
Reset Your Settings. After installation, reset the time (if necessary), normalize the windows, and reset the ESP light.
- On newer vehicles, the time may reset automatically. For window normalization, roll up the window and hold the button for 5 seconds. To reset the ESP light, turn the steering wheel from lock to lock until the light disappears.
Congratulations! You've successfully replaced the battery in your Mercedes-Benz!
Helpful Tips
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When removing a battery located under the hood, place a towel or blanket over the fender to prevent any potential body or paint damage. Batteries can be heavy and awkward to handle during removal, increasing the risk of damage.
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Be cautious of the following: installing the battery incorrectly, over-tightening battery cables, and ensuring that the ratchet or wrench does not make contact with the body when loosening the battery cable nut.
