How to Change the Auxiliary Battery on a Mercedes ML350

On high-end vehicles like the Mercedes ML, an auxiliary battery is installed to ensure that services remain available even during high electrical demand. Let's see how to change it and where it is located.

On our Mercedes ML, the battery is not located in the engine bay but under the passenger seat. To access it, slide the seat all the way back, remove the mat, and lift the plastic cover.

Underneath, you will find a compartment with a vent, which we will remove, and a metal plate that held the vent in place. Below this is the starter battery.

Remember that when working on the battery, the keys must not be in the ignition, and all electrical request buttons must be in the "off" position for safety. Now, remove the negative terminal, then the positive; disconnect the battery ventilation.

Next, using a 13 mm spanner, remove the bolts securing the battery. Remove the battery retainers and take it out of its housing.

Now, access the auxiliary battery located to the side. Always disconnect the negative terminal first, then the positive.

This battery costs around £40 when purchased from major e-commerce platforms. Now, simply reverse the process to reinstall the auxiliary battery, reposition the starter battery, the plate, the vent, the plastic cover, the mat, and put the seat back in place.

Job done.