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  • V-Class
  • 03/2021
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Starting assistance and charging the 12 V battery
WARNING Risk of explosion from a frozen battery

A discharged battery may freeze at temperatures slightly above or below freezing point.

During starting assistance or battery charging, battery gas can be released.

Always allow a battery to thaw before charging it or performing starting assistance.

If the warning/indicator lamps do not light up in the instrument cluster at temperatures around or below freezing, it is highly probable that the discharged battery has frozen.

In this case, observe the following points:
  • do not give the vehicle starting assistance or charge the battery

  • the service life of a battery that has been thawed may be reduced drastically

  • the starting behaviour may deteriorate, particularly at low temperatures

  • it is recommended that you have a thawed battery checked at a qualified specialist workshop

WARNING Risk of explosion during charging process and starting assistance

During the charging process and starting assistance, the battery may release an explosive gas mixture.

Avoid fire, naked flames, creating sparks and smoking.
Make sure there is sufficient ventilation.
Do not lean over a battery.
WARNING Danger of chemical burns from the battery acid

Battery acid is caustic.

Avoid contact with the skin, eyes or clothing.
Do not lean over the battery.
Do not inhale battery gases.
Keep children away from the battery.
Immediately rinse battery acid off thoroughly with plenty of clean water and seek medical attention immediately.
Starting assistance
NOTEDamage caused by numerous or extended attempts to start the engine

Numerous or extended attempts to start the engine may damage the catalytic converter due to non-combusted fuel.

Avoid numerous and extended attempts to start the engine.

Do not use a rapid charging device to start the vehicle. If your vehicle's battery is discharged, the engine can be jump-started from another vehicle or from a donor battery using jump leads. For this purpose, the vehicle has a jump-start connection point in the engine compartment.

When jump-starting, observe the following points:
  • The battery is not accessible in all vehicles. If the other vehicle's battery is not accessible, starting assistance is to be provided using a donor battery or a starting assistance device.

  • You may only jump-start the vehicle when the engine and exhaust system are cold.

  • Do not start the engine if the battery is frozen. Let the battery thaw first.

  • Starting assistance may only be provided using batteries with a nominal voltage of 12 V.

  • Only use jump leads that have a sufficient cross-section and insulated terminal clamps.

  • If the battery is fully discharged, attach the donor battery for a few minutes before attempting to start. This charges the discharged battery a little.

  • Make sure that the two vehicles do not touch.

Jump leads and further information regarding starting assistance can be obtained at any qualified specialist workshop.

Ensure the following before connecting the jump lead:
  • The jump leads are not damaged.

  • Parts of the terminal clamps which are not insulated do not come into contact with other metal parts while the jump leads are connected to the battery.

  • The jump leads do not touch moving parts when the engine is started and while it is running, such as the V-belt pulley or the fan.

Apply the parking brake.
Vehicles with automatic transmission:
shift the transmission to position .
Vehicles with manual transmission:
shift to neutral.
Switch off all electrical consumers, e.g. audio device, blower.
Switch off the ignition immediately and remove the key.
Open the bonnet More.
Connecting and disconnecting the jump lead
Example: jump-start connection point
Push contact protection cover of the jump-start connection point towards the rear of the vehicle against the spring pressure as far as it will go.

The jump-start connection point is visible.

Terminal connection diagram
Remove the cover from positive terminal of the donor battery.
Connect the positive terminal clamp of the jump lead to positive terminal of the donor battery, and then to positive terminal of the jump-start connection point.
Connect the negative terminal clamp of the jump lead to negative terminal of the donor battery, and then to earth contact of your own vehicle.
Start the engine of the donor vehicle and run it at idling speed.
Insert the key into the ignition lock, start the engine and let it run for several minutes.
Before disconnecting the jump leads, switch on an electrical consumer in your own vehicle, e.g. the rear window heater or the lighting.
Disconnect the negative terminal clamp of the jump lead from earth contact and then from negative terminal of the donor battery.
Disconnect the positive terminal clamp of the jump lead from positive terminal on the jump-start connection point, and then from positive terminal of the donor battery.

Contact protection cover is automatically returned forwards to its original position by the spring force and the jump-start connection point is closed.

Position the cover on positive terminal of the donor battery.
Have the battery checked at a qualified specialist workshop.
Charging the 12 V battery
NOTE Damage to the electronics caused by non-approved charging devices

Charging a fitted battery with a battery charger which has not been approved by Mercedes-Benz can damage the on-board electronics.

Only use a battery charger which has been approved by Mercedes-Benz and which permits charging the battery when it is fitted in the vehicle.
Only charge the battery using the jump-start connection point.

A battery charger specially adapted for Mercedes-Benz vehicles and tested and approved for Mercedes-Benz is available as an accessory.

Further information is available from any Mercedes-Benz Service Centre. Read the operating instructions for your charger before charging the battery.

Recharge the battery more frequently if you use the vehicle mainly for short trips and/or drive at low outside temperatures.

Connect the battery charger to the positive terminal and earth contact in the same order as when connecting the donor battery in the jump-starting procedure.

If a battery is not fitted and not in service, you should charge it every three months. This helps to counteract self-discharging and prevent damage to the battery.

12 V battery care
NOTE Battery discharge due to leakage currents

Dirty battery terminal clamps and battery surfaces cause leakage currents. This can lead to the battery discharging.

Keep the battery terminals and battery surfaces clean and dry.
NOTE Damage to the battery housing due to improper cleaning

If you use cleaning agents containing fuel, these can damage the battery housing.

Do not use cleaning agents containing fuel.
NOTE Damage to the battery due to self-discharge

If dirt gets into the battery cell, the self-discharge of the battery is increased and the battery can be damaged.

Only clean the battery with the cell caps screwed in.

Observe the following points on battery care:

Regularly check the battery terminals and the fastening of the negative cable to the chassis to ensure that they are firmly seated.
Lightly grease the undersides of the battery terminal clamps with acid-resistant grease.
Only clean the battery housing with commercially available cleaning agents.