Jump-starting a car safely comes down to one thing people most often get wrong: the order you connect the four cable ends in. Connect positive-to-positive first, then negative to the dead car’s engine block or a metal bracket — never its negative terminal directly — and the reverse order when disconnecting. Getting this sequence backward is the most common cause of sparks, minor electronics damage, or a small battery explosion from ignited hydrogen gas.
What You Need
- A set of jumper cables, or a portable jump-start battery pack (which skips the need for a second running car entirely and is worth owning if you drive an older car regularly).
- A second vehicle with a healthy, charged battery, if not using a jump pack.
- Both vehicles positioned close enough that the cables reach comfortably without either car touching the other.
Step-by-Step: Connecting the Cables
A battery under charge can vent hydrogen gas, which is explosive near a spark. Connect cables in the correct order (covered below), never let the clamps touch each other, and keep sparks and flames away from the battery. On hybrid or electric vehicles, check the owner’s manual first — some models have a dedicated jump-start terminal rather than direct access to the 12V battery.
- Turn off both vehicles and put them in Park or Neutral with the handbrake on.
- Connect the red (positive) clamp to the dead battery’s positive terminal.
- Connect the other red (positive) clamp to the good battery’s positive terminal.
- Connect the black (negative) clamp to the good battery’s negative terminal.
- Connect the final black (negative) clamp to an unpainted metal surface on the dead car’s engine block or chassis — not the dead battery’s negative terminal. This last connection is where a spark is most likely, and grounding it away from the battery itself keeps that spark away from any hydrogen gas the battery may be venting.
Starting the Car
- Start the working vehicle and let it run for a couple of minutes.
- Attempt to start the dead vehicle. If it doesn’t start on the first try, wait a minute and try again rather than cranking repeatedly, which can overheat the starter.
- Once started, let it run for several minutes before disconnecting, to build some charge back into the battery.
Disconnecting: Reverse the Order
Remove the cables in the exact reverse sequence from how they went on:
- Black clamp from the dead car’s chassis/engine block.
- Black clamp from the good car’s negative terminal.
- Red clamp from the good car’s positive terminal.
- Red clamp from the dead car’s positive terminal.
Once running, drive for at least 15–20 minutes, ideally at a steady speed rather than a lot of stop-start traffic, to let the alternator rebuild the battery’s charge.
If the Car Won’t Stay Running or Won’t Start at All
A jump start gets a car going, but it doesn’t fix why the battery was dead in the first place. If the car dies again shortly after, or won’t start even with a jump, see our battery keeps dying overnight guide and car cranks but won’t start guide — a battery that won’t hold a jump at all often means it needs replacing rather than just recharging.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
When to See a Mechanic
If jump-starting becomes a recurring need rather than a one-off, that pattern itself is worth diagnosing — see our battery drain guide for tracking down a parasitic drain, or have the battery and alternator tested, since a battery nearing the end of its life often shows exactly this pattern before failing completely. More in our electrical problems section.
Frequently Asked Questions
What order do you connect jumper cables in?
Positive to the dead battery first, then positive to the good battery, then negative to the good battery, then negative to an unpainted metal surface on the dead car — not its battery terminal directly. Disconnect in the reverse order.
Why shouldn’t I connect the last cable to the dead battery’s negative terminal?
That final connection is where a spark is most likely to occur, and a battery can vent flammable hydrogen gas. Grounding the last connection away from the battery itself keeps any spark away from that gas.
How long should I let the car run after a jump start?
At least 15–20 minutes of driving, ideally at a steady speed, to let the alternator rebuild the battery’s charge before turning the engine off again.
Can I jump-start a hybrid or electric car the same way?
Check the owner’s manual first — many hybrids and EVs have a dedicated jump-start terminal separate from the main battery, rather than direct access like a conventional car.
What if the car won’t start even with a jump?
That often means the battery itself needs replacing rather than just recharging, or that a deeper electrical fault is preventing the engine from starting regardless of battery charge.
