Mercedes-Benz A Series 2015 Owner's Manual page 352

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 second battery using jump
leads. Observe the following points:
The battery is not accessible in all vehicles. If the other vehicle's battery is not accessible,
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jump-start the vehicle using a second battery or a jump-starting device.
Do not start the engine if the battery is frozen. Let the battery thaw first.
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Jump-starting may only be performed using batteries with a nominal voltage of 12 V.
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Only use jump leads that are not damaged and have a sufficient cross-section and insulated
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terminal clamps.
Make sure that the two vehicles do not touch.
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Make sure that:
The jump leads are not damaged.
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Non-insulated parts of the terminal clamps do not come into contact with other metal parts
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while the jump leads are connected to the battery.
The jump leads cannot come into contact with parts which can move when the engine is
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running, such as the V-belt pulley or the fan.
Secure the vehicle by applying the electric parking brake.
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Manual transmission: depress the clutch pedal fully and shift to neutral.
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Automatic transmission: shift the transmission to position P.
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Turn the key to position 0 in the ignition lock and remove it.
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Switch off all electrical consumers, e.g. rear window heating, lighting etc.
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Open the bonnet.
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Position number B identifies the charged battery of the other vehicle or an equivalent jump-
starting device.
Press together cover : of positive clamp ; and slide it back.
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Connect positive terminal ; on your vehicle to positive terminal = of donor battery B
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using the jump lead, beginning with your own battery.
Jump-starting
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