Mercedes-Benz 2013 CLA Owner's Manual page 309

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,
R
jump-start the vehicle using a second battery or a jump-starting device.
Vehicles with a petrol engine: only jump-start the vehicle when the engine and exhaust
R
system are cold.
Do not start the engine if the battery is frozen. Let the battery thaw first.
R
Jump-starting may only be performed from batteries with a nominal voltage of 12 V.
R
Only use jump leads that have a sufficient cross-section and insulated terminal clamps.
R
If the battery is fully discharged, leave the battery that is being used to jump-start connected
R
for a few minutes before attempting to start. This charges the empty battery a little.
Make sure that the two vehicles do not touch.
R
Make sure that:
the jump leads are not damaged.
R
bare parts of the terminal clamp do not come into contact with other metal parts while the
R
jump leads are connected to the battery.
the jump leads cannot come into contact with parts which can move when the engine is
R
running, such as the V-belt pulley or the fan.
X
Secure the vehicle by applying the electric parking brake.
X
Manual transmission: depress the clutch pedal fully and shift to neutral.
X
Automatic transmission: shift the transmission to position P.
X
Turn the key to position 0 in the ignition lock and remove it.
X
Switch off all electrical consumers, e.g. rear window heating, lighting etc.
X
Open the bonnet.
Jump-starting
Z
307