Mazda Mazda3 2019 Owner's Manual page 478

If Trouble Arises
Battery Runs Out
Connect the negative lead to a good ground point away from the battery:
Connecting the end of the second jumper lead to the negative (–) terminal of the discharged
battery is dangerous.
A spark could cause the gas around the battery to explode and injure someone.
Route the jumper leads away from parts that will be moving:
Connecting a jumper lead near or to moving parts (cooling fans, belts) is dangerous. The lead
could get caught when the engine starts and cause serious injury.
CAUTION
Use only a 12 V booster system. You can damage a 12 V starter, ignition system, and other
electrical parts beyond repair with a 24 V power supply (two 12 V batteries in series or a 24 V
motor generator set).
1. Move the booster vehicle so that its battery is as close as possible to your vehicle's
battery.
2. Make sure that the power such as for the headlights and air conditioner is turned off.
3. Remove the battery cover.
4. Turn off the booster vehicle's engine and connect the jumper leads in the following
order.
Make sure that the jumper leads are securely connected so that they do not disconnect
due to engine vibrations.
1st lead
Positive (+) terminal on the discharged battery
Positive (+) terminal on booster vehicle's battery
2nd lead
Negative (-) terminal on booster vehicle's battery
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