# Jump-Starting a Battery Part of the Automotive Maintenance Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/automotive-maintenance/guide/index.md) *8. Ignition & Electrical* > **8d.** Demonstrate how to safely connect jumper cables to your car battery. A dead battery is one of the most common roadside problems. Knowing how to safely jump-start a vehicle is a practical skill that every driver — and every Scout — should have. The process is straightforward, but the order of the connections matters for safety. > **Safety First!** > > Car batteries produce hydrogen gas, which is flammable. A spark near the battery can cause an explosion. This is why the last connection is made away from the dead battery — to keep any spark far from the hydrogen gas. Follow the connection order exactly. ### What You Need - A set of **jumper cables** (also called booster cables) — heavier gauge cables (4 to 6 gauge) are better because they carry more current. - A **donor vehicle** with a charged battery of the same voltage (12V for most passenger vehicles). - Both vehicles should be **parked close enough** for the cables to reach, but **not touching** each other. ### Step-by-Step: Connecting Jumper Cables **Jump-Start Procedure** — Follow this order exactly - [ ] Turn off both vehicles. Remove the keys from the ignition. Turn off all accessories (lights, radio, AC). - [ ] Identify the positive (+) and negative (-) terminals on both batteries. Positive terminals are usually marked with a "+" sign and may have a red cover. Negative terminals are marked with a "-" sign and may have a black cover. - [ ] Connect the RED (positive) cable to the POSITIVE (+) terminal of the DEAD battery. - [ ] Connect the other end of the RED cable to the POSITIVE (+) terminal of the GOOD battery. - [ ] Connect the BLACK (negative) cable to the NEGATIVE (-) terminal of the GOOD battery. - [ ] Connect the other end of the BLACK cable to an UNPAINTED METAL SURFACE on the dead vehicle's engine block — not to the dead battery's negative terminal. A bolt or bracket on the engine works well. This is the ground connection. - [ ] Start the donor vehicle and let it run for 2 to 3 minutes. - [ ] Try to start the dead vehicle. If it does not start, wait a few more minutes and try again. - [ ] Once the dead vehicle is running, disconnect the cables in REVERSE order: black from engine block, black from good battery, red from good battery, red from dead battery. - [ ] Drive the jump-started vehicle for at least 15 to 20 minutes to allow the alternator to recharge the battery. ### Why the Last Connection Goes to the Engine Block The final connection (the black cable to the engine block of the dead vehicle) is made **away from the battery** on purpose. When you make this last connection, a small spark is likely. If that spark happened right next to the battery, it could ignite the hydrogen gas that dead batteries sometimes vent. By connecting to the engine block instead, the spark occurs safely away from the battery. > **Be Prepared! The Dead Vehicle Will Not Start After Jump-Starting** > > If the dead vehicle cranks slowly or does not start after several minutes of charging: > > - Check that all cable connections are tight and making good contact (corrosion on terminals can block the flow). > - Make sure the donor vehicle is running at a slightly elevated RPM (about 1,500 RPM) to provide more charging current. > - If the battery is very old or severely discharged, it may need to charge for 10 to 15 minutes before attempting to start. > - If the vehicle still will not start, the battery may be too damaged to hold a charge and may need to be replaced. > **Tip** > > Consider carrying a **portable jump starter** (also called a jump pack) in your vehicle. These battery-powered devices can jump-start a car without needing a second vehicle. Many modern jump packs are small enough to fit in a glove compartment and can also charge your phone. ![A clear diagram showing two cars facing each other with jumper cables connected in the correct order: red cable on dead battery positive, red on good battery positive, black on good battery negative, and black on dead car engine block — with numbered steps](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/automotive-maintenance/guide/jumper-cable-connection?v=4c6d1f5f) ![Two Scouts jump-starting a car in a parking lot, one connecting the jumper cable to the engine block while an adult supervises nearby](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/automotive-maintenance/guide/jump-start-action?v=69d87515) Video: [How to Properly Jump Start a Car](https://youtu.be/iI1o2hNy2hE?si=t_Z0kfFFLqNt1lkQ) [Scout Life — How to Jump Start a Dead Battery](https://scoutlife.org/features/150888/how-to-jump-start-a-dead-battery/): Step-by-step guide from Scout Life magazine with helpful illustrations. --- - Previous: [Firing Order & Spark Gap](https://merit-badge.university/merit-badges/automotive-maintenance/guide/req8b/index.md) - Next: [Electric Vehicles](https://merit-badge.university/merit-badges/automotive-maintenance/guide/req8e/index.md)