Mercedes-Benz G-Class Operator's Manual page 246

Jump-starting
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Particularly avoid fire, open flames, creating sparks and smoking. Ensure there is sufficient ven-
tilation while charging and jump-starting. Do not lean over a battery.
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WARNING
During the charging process, a battery produces hydrogen gas. If a short circuit occurs or sparks
are created, the hydrogen gas can ignite. There is a risk of an explosion.
Make sure that the positive terminal of a connected battery does not come into contact with
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vehicle parts.
Never place metal objects or tools on a battery.
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It is important that you observe the described order of the battery terminals when connecting
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and disconnecting a battery.
When jump-starting, make sure that the battery poles with identical polarity are connected.
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It is particularly important to observe the described order when connecting and disconnecting
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the jumper cables.
Never connect or disconnect the battery terminals while the engine is running.
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WARNING
A discharged battery can freeze at temperatures below freezing point. When jump-starting the
vehicle or charging the battery, gases can escape from the battery. There is a risk of an explosion.
Allow the frozen battery to thaw out before charging it or jump-starting.
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Avoid repeated and lengthy starting attempts. Otherwise, the catalytic converter could be
damaged by the non-combusted fuel.
If the warning and indicator lamps do not light up on the instrument cluster when temperatures are
low, it is probably because the discharged battery has frozen. In this case, you may neither charge
the battery nor jump-start the vehicle. The service life of a thawed-out battery may be shorter. The
starting characteristics can be impaired, particularly at low temperatures. 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, jump-
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start the vehicle using a second battery or a jump-starting device.
You may only jump-start the vehicle when the engine and exhaust system are cold.
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Do not start the engine if the battery is frozen. Let the battery thaw first.
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Jump-starting may be performed only using 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 for
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a few minutes before attempting to start. This charges the battery slightly.
Make sure that the two vehicles do not touch.
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Make sure that:
the jumper cables are not damaged.
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when the jumper cables are connected to the battery, uninsulated sections of the terminal clamp
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do not come into contact with other metal sections.
the jumper cables 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.