Mercedes-Benz G-Class Operator's Manual page 306

Jump-starting
304
If the indicator/warning lamps do not light up at temperatures around or below freezing point,
the discharged battery is likely to be frozen (a commonplace scenario). In this case, do not
jump-start the vehicle or recharge the battery.
Once the battery has thawed out, its service life may be dramatically reduced.
The starting characteristics can be impaired, particularly at low temperatures.
It is recommended that you have the thawed out battery checked at a qualified specialist
workshop.
Do not start the vehicle using a rapid charging device. If your vehicle's battery is discharged,
the engine can be jump-started from another vehicle or from a second battery using jumper
cables. 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.
Vehicles with a gasoline engine: only jump-start the vehicle when the engine and exhaust
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system are cold.
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 from batteries with a nominal voltage of 12 V.
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Only use jumper cables which have a sufficient cross-section and insulated terminal clamps.
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If the battery is fully discharged, leave the battery that is being used to jump-start connected
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for a few minutes before attempting to start. This charges the empty battery a little.
Make sure that the two vehicles do not touch.
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Make sure that:
the jumper leads are not damaged.
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when the jumper cables are connected to the battery, uninsulated sections of the terminal
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clamp do not come into contact with other metal sections.
The jumper cables cannot come into contact with parts such as the pulley or the fan. These
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parts move when the engine is started and while it is running.
Apply the parking brake.
X
Move the selector lever to position P.
X
Switch off all electrical consumers (e.g. radio, blower, etc.).
X
Open the hood (
X
page 283).
Y