This article goes over the High Voltage (HV) Battery (A100), how it works, and common problems. The first-generation 128v 6.5ah hybrid battery is used in BMW ActiveHybrid and Mercedes-Benz S400 W221 and uses thirty-five Li-Ion cells similar to these Saft VL6 cells.
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The high voltage battery is costly. In some cases, the hybrid battery costs more than the resale value of the vehicle. A new Mercedes-Benz hybrid battery costs over $10,000, while a used unit can be found for around $3,000 to $5,000.
Replacing the high voltage battery is relatively easy but should only be completed by a trained technician due to the increased risk of a fatal accident.
This article is for information purposes only. The hybrid battery is hazardous and can lead to fatal accidents.
A hybrid battery should not be opened up or repaired by untrained individuals.
Lithium-ion batteries are a safety hazard and extremely dangerous if overcharged.
The most common problems with Mercedes-Benz S400 hybrid vehicles are the failure of the power electronic module and the failure of the hybrid battery. To fix either one of these problems at the dealership, you will spend between $9,000 to $12,000.
Battery Management System (BMS) Failure. BMS is integrated inside the hybrid battery.
Critically Low Charge Level of the Hybrid Battery
Bad Li-ion Cell - One faulty cell can lead to the hybrid battery shutting off. The battery shown above has 35 cells—a nominal voltage of 3.7 volts and a max of 4.1 volts per cell.
Contractor Issue - Contactors open and close the high voltage circuit. They are located inside the high voltage hybrid battery and can fail.
Other possible problems with Mercedes-Benz hybrid vehicles are:
Inside the hybrid battery, you will also find the BMS (Battery Management System - N82/2). The BMS manages the charging of the hybrid battery.
A critical function is to ensure that each of the 35 li-ion cells is balance-charged, which means that none of the cells should have a high or low charge level than the rest. To be balance charged, all the cells must be within 0.03 Volt of each other.
Common fault codes that show up as stored or current in the battery management module (SG-BMS):
180F00 - The high voltage battery has a malfunction during the recovery phase.
0BBD00 - The limit value for the difference between cell voltages in the high voltage battery module exceeded.
0BBE00 - The cell voltages in the high voltage battery module are different.
0A7D00 - The charge level of the high voltage battery module is low.
180C00, 180500 - The hardware monitoring function has detected a fault in the control unit.
0A1F04 - There is an internal fault in the control unit battery. There is an internal fault.
0AE886 - The temperature sensor D of the high voltage battery has an electrical fault. There is an incorrect signal.
0ACA86 - The temperature sensor C of the high voltage battery has an electrical fault. There is an incorrect signal.
0AC586 - The temperature sensor B of the high voltage battery has an electrical fault. There is an incorrect signal.
0A9B86 - The temperature sensor A of the high voltage battery has an electrical fault. There is an incorrect signal.
0A1F96 - There is an internal fault in the control unit battery. There is an internal component fault.
0A1F00 - There is an internal fault in the control unit battery.
0A7F00- Hybrid Battery Pack Deterioration
161A52 - ECU In-Plant Mode Active not activated
0AE500 - Hybrid Battery Negative Contractor Control Circuit Range Performance
0ADA00 - Hybrid Battery Positive Contactor Control Circuit Range Performance
0ADE00 Hybrid Battery Negative Contractor Control Circuit Range Performance
When you connect a multi-system OBD-II scanner and read the BMS Control Module codes, you communicate via the CAN network with the N82/2 module inside the hybrid battery.
The BMS monitors the status of the interlock circuit, the temperature of the cells, the voltage of the hybrid battery, and the contractors' status.
The BMS also monitors the cooling system for the hybrid battery, which runs off the electric A/C compressor that also cools the cabin.
Hybrid Battery Safety Fuse
Inside the hybrid battery, you will find a fuse in series between cells 18 and 19.
The fuse's main function is to avoid overheating and the explosion of the hybrid battery if there is a short circuit on the high voltage system, which is possible in case of an accident.
If the first generation high voltage battery, the battery found on the W221 unit needs to be replaced if the fuse has blown because the battery is not designed to be opened or repaired.
In the newer W222 S-Class, the battery can be opened by a trained technician and can be repaired.
Contractors A100s1 are installed inside the hybrid battery.
Think of the contractors as an on / off switch inside the hybrid battery controlled by the ECU and BMS. When you turn on the ignition, the contractors close, which powers up the high voltage system.
When the ignition is turned off, the contractors open up, and the system automatically turns off.
Why does my hybrid battery not charge 100%?
The ideal charge level for the hybrid battery is not 100%. Li-ion and LiPo batteries' ideal charge levels are 50%-70% of maximum capacity.
In this range, the HV li-ion performs the best and lasts the longest. Do not expect to see a 100% charge on a hybrid vehicle. Even on fully electric vehicles, regularly charging the battery to 100% is not recommended, or the battery's life will decrease significantly.
Li-ion does not need to be fully charged, as is the case with lead acid, nor is it desirable to do so. It is better not to fully charge because the high voltage shortens the battery life.
You will notice that your hybrid battery will fluctuate between 40% and 80%, which is perfectly normal.
HV Battery Charge Levels
Here is a breakdown of the optimal state of charge (SOC) level on a li-ion battery:
0-30% - Extremely low charge level
30%-50% - Low charge level
50%-90% - Normal charge, operating level
90%-100% - High charge level
In fact, if the battery charge level is below 28%, the vehicle will no longer start. While the hybrid battery discharges very slowly, it is possible that a vehicle that has been parked for a very long time can reach under 28% SOC.
The hybrid battery on a W221 has 35 individual cells rated at 4.1 Volt maximum. Typically those batteries operate in the 3.5V to 3.7V range.
Therefore the maximum charge level reaches a voltage of 12.9.5. Simultaneously, the extremely low range when the battery reaches 0% is, in fact, 115 volts or 3.28 Volt per cell. Even though the battery voltage can drop below 115V, it is considered fully discharged and will engine start will be disabled.
At 80% SOC, the voltage of the hybrid battery should be 130 volts.
How to troubleshoot a hybrid Mercedes-Benz
Even if there is damage or burn to the board, the reader can access the module and determine the error.
Connect the scanner to the OBD port.
Use Electronic Motor Control Unit Menu to check Motor ECM faults.
Procedures for using a scanner to diagnose HV battery not charging.
Connect the charger’s positive terminal to the 12v input Battery input and connect the negative to the ground.
Connect the scanner to the ODB2 port and turn on the ignition.
Check the "Status of Contractor on the menu." If the contractor is open, then most probably, this is the cause of the battery not charging.
Check above via DC-to-DC converter Control unit Menu.
Read Data Stream
Check the operating state status; if the status is passive, the system is not charging the HV hybrid battery.
Verify the status of “Voltage of High voltage On-Board Electrical System.” It should be between 48 v to 120.
Follow the procedures to charge the HV system if the “Voltage of High voltage On-Board Electrical System” status equals 0.
Clear the codes
to go to the battery management system.
Go to actuation test.
Go to actuation of contractors menu.
These procedures will generally change the status of contractors from open to close if there is no other error is associated with it.
You will see the “Voltage of High voltage On-Board Electrical System” would slowly rise.
How to ship a high voltage lithium battery?
The high voltage lithium-ion battery is classified as a hazardous material. They should be handled with care and should not be dropped. Your country may have different regulations, but the most common classification for a hybrid battery is the UN 3480 Lithium-ion battery, Class 9, PG II.
It is recommended to ship a li-ion battery at 30 to 40 % state-of-charge rather than a full charge.
Do not ship a hybrid battery if the housing is damaged.
If you are having issues with the hybrid, please "contact the YOUCANIC" team with any questions that you may have.
We can help you troubleshoot the problem FREE of charge as long as you send us the codes. We need the codes from these four modules:
Power Electronics Module.
Once we have the codes, we can tell you if you have a bad power electronic module, hybrid battery, or both.
If your vehicle is at the dealership or mechanic, ask them for the list of codes and send them to us.
I have been working on vehicles for over 20 years. In 2016, I decided to start YOUCANIC so that I can empower vehicle owners all over the world. Currently, I hold an ASE certification on G1 Automotive Maintenance and Light Repair.
Mercedes-Benz Hybrid Problems This article goes over the High Voltage (HV) Battery (A100), how it works, and common problems. The first-generation 128v 6.5ah hybrid battery is used in BMW ActiveHybrid and Mercedes-Benz S400 W221 and uses thirty-five Li-Ion cells similar to these Saft VL6 cells.