SMART Fortwo 2015 Owner's Manual page 193

If the indicator/warning lamps do not light up at low temperatures, it is very likely that the
discharged battery has frozen. In this case you may neither jump-start the vehicle nor charge
the battery. The service life of a battery that has been thawed may be reduced. The starting
characteristics may be impaired, especially at low temperatures. Have the thawed battery
checked at a qualified specialist workshop.
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.
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 only be performed from batteries with a nominal voltage of 12 V.
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Only use jump leads that 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 con-
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nected 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 jump leads are not damaged.
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Bare parts of the terminal clamp do not come into contact with other metal parts while the
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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 wiper rods or the fan.
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Secure the vehicle using the parking brake.
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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 service cover.
Jump-starting
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