48V mild-hybrid battery warnings diagnosed

Which Mercedes models have a 48V battery?

The 48V mild-hybrid system is fitted to a number of recent Mercedes models. Mercedes’ technical guidance on 48V faults covers, among others:

• E-Class (213 and 238)
• CLS (257)
• GLE and GLS (167)
• AMG GT 4-door (290)
• the A-Class family (model series 177, 118 and 247)

The C-Class (206) and S-Class (223) use a later version of the system, which is tested differently. If you are not sure whether your car has a 48V battery, put the registration in the enquiry form and we will check. For other Mercedes work, see our Mercedes specialist page.

What are the symptoms?

Mercedes lists these signs of a fault in the 48V system:

• a yellow or red 48V battery message on the display
• the engine will not start
• limp-home running with reduced power
• the air conditioning not cooling
• the engine warning light

On the E-Class, the owner’s manual message for a flat 48V battery says its charge level is too low and the engine can no longer be started.

When you book, tell us the colour and wording of the message, when it first appeared and whether the car still starts.

What causes a 48V battery fault?

Mercedes names several distinct causes:

• a software fault in the 48V battery or its DC/DC voltage converter
• a short circuit in one of the other 48V components
• failure of the cooling element inside the battery
• the battery disconnecting itself
• loose ground connections

This is why the warning on its own does not tell us which part, if any, has failed. It is also a different system from the auxiliary battery: if your message mentions the auxiliary battery, see our auxiliary battery malfunction page.

How do you confirm the cause before fitting parts?

A fault code is not a repair. Before we quote for any parts, we:

• check the recall status, then the 12V battery and supply
• read which 48V fault is stored, because each one leads to a different remedy
• inspect the ground connections and terminal bolts
• where a short circuit is suspected, disconnect the 48V components one at a time to find it

The work is done by technicians qualified to work on electric and hybrid vehicles.

We then show you what we found and send a written price. No part is fitted until you approve it in writing.

What does the repair involve?

It depends on the cause. Mercedes’ guidance is to replace the 48V battery only when the guided test says so, so a warning does not automatically mean a new battery.

Some of the causes are software faults rather than failed parts. We tell you which cause we found and what its remedy involves before any work starts. Once the work is done, we verify the repair, including a road test where appropriate.

How long does a 48V battery repair take?

It depends on what the tests find, because each cause has a different remedy.

Before any work starts, you get a written price and a promised time for your next update. If the car needs to stay with us, ask about a courtesy car when you book.

Is there a recall for the 48V system?

The DVSA lists these recalls for 48V ground connections:

• R/2023/246: C-Class built January 2019 to April 2023
• R/2023/056: C-Class
• R/2024/173: GLE and GLS
• R/2022/133: GLE and GLS

Whether a recall applies depends on the individual car, so check your registration on gov.uk. Mercedes-Benz UK’s own vehicle check also shows non-safety service measures. Recall work is done by the manufacturer’s network, not by us.