Mercedes MMA Battery

A look at the Mercedes MMA battery that will appear in the 2025 CLA at launch. MMA stands for Mercedes-Benz Modular Architecture and the platform has both ICE and EV variants.

Mercedes Vision EQXX

Mercedes note that a lot of learning came from the research vehicle EQXX. The EQXX was very efficient, thus reduing the demand on the battery pack and delivering an overall more competitive product.

A rectangular flat battery pack is the simplest and most cost effective form for an electric vehicle battery. The power electronics are arranged on the top of the pack. Note that this is an 800V architecture and with efficiency as a key driver they have minimised the length of HV cables.

Modules

• 192 cells
• Arranged in 4 groups (modules) of 48 cells

The pack frame is described as being made from steel, however, when you look in detail the internal bracing structures are diecast aluminium. In the next image you can see the local CSC boards on the modules on the left hand side of the pack. In the case of the modules on the right hand side they have been rotated 180° thus allowing the simple busbar connections.

All four modules appear to be exactly the same: 48 cells in series.

The cooling is integrated into the base frame and hence means all cooling joints and connections are external to the HV system. A significant HV safety design, but perhaps not optimal in terms of thermal performance.

Cells

Safety

It appears that the HV control system has both switchable contactors and a pyro switch:

In the event of danger, the HV system can be automatically switched off and disconnected from the battery. A distinction is made between reversible and irreversible disconnection. Reversible disconnection takes place in the event of minor accidents. The high-voltage system can then be reconnected if an insulation measurement carried out by the vehicle beforehand does not detect a fault. This means that vehicles that are still roadworthy can continue to be driven. The high-voltage system is only irreversibly switched off in the event of serious accidents, in which the vehicle is usually no longer drivable anyway. It cannot be reactivated without repair in a specialised workshop. 

New Cell Chemistries [1]

In the image of the inside of the battery pack we see the arrangement to minimise busbars and a simple bridge between the two modules at the front of the pack. This suggests that the irreversible switch is not positioned at the pack midpoint.

In the case of mechanical impact there are the normal static and crash impact requirements. In addition Mercedes use a jacking test to mimic road debris requirements:

Mercedes-Benz uses another special test bench procedure to test the so-called touchdown management. This refers to the design precautions taken to prevent damage to the underbody caused by touching down, for example when driving over kerbs. During the test, a ram is pressed into the vehicle floor with a force of several tonnes. This also tests whether there is a risk of intrusion from foreign objects lying on the road, such as lost towbars.

Environment

Some big claims in the environmental performance of this battery pack, great to see, but would be good to see a completely independent audit.

1. More sustainable product design already in the development phase
2. CO₂ neutrality as a central award criterion in the supply chain
3. Balance sheet CO2-neutral production in our own plants worldwide
4. Green Charging in Europa, USA/ Kanada mit Mercedes me Charge
5. Use of factory-repaired batteries in the vehicle
6. Stationary energy storage units from Mercedes-Benz Energy give batteries a second life
7. Closing the material cycle through recycling

References

1. New cell chemistries: high energy density, fast charging and excellent performance, Mercedes-Benz Media
2. Deep Dive MMA: How Mercedes wants to score points with efficiency with the electric CLA, electrive
3. Mercedes’ electric CLA to use LFP cells from BYD, electrive