GarageDex

How to Jump Start a Car

Reviewed by GarageDex editorial

GarageDex's guide to jump starting covers the sequence that matters for safety: the last clamp goes to bare metal on the dead car, not to its battery, so any spark happens away from the battery's hydrogen gas. It also covers jump packs, which have replaced cables for most people, and the cars you should not jump the usual way.

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Step by step with cables

  1. Park the working car close enough for the cables to reach, but not touching. Both cars off, in Park or in gear with the parking brake set, all accessories off.
  2. Connect one red clamp to the positive (+) terminal of the dead battery, then the other red clamp to the positive (+) of the good battery.
  3. Connect one black clamp to the negative (-) of the good battery.
  4. Connect the last black clamp to bare, unpainted metal on the dead car's engine or chassis, away from the battery and any moving parts. Not to the dead battery's negative post.
  5. Start the working car and let it run 2 to 3 minutes. Then start the dead car. If it only clicks, wait a few more minutes and try again.
  6. Once it runs, remove the clamps in reverse order: black from the chassis, black from the good battery, red from the good battery, red from the dead battery. Drive at least 20 to 30 minutes.

Before you connect anything

Do not jump a battery that is cracked, leaking, or frozen (a bulging case in freezing weather). Do not let the red and black clamps touch each other while any clamp is connected. Make sure the two cars are not touching. If the terminals are heavily corroded, clean them enough for the clamps to bite on metal.

What you need

Either a set of cables and a second car, or a portable lithium jump pack, which is what most drivers should carry now: it works alone, fits in the glovebox, and doubles as a phone charger.

Tools used in this guide

  • Portable jump starterMatch the peak-amp rating to your engine size; diesels and big V8s need moreView on Amazon
  • Jumper cablesHeavier gauge (lower number) carries more current; 4 to 6 gauge for full-size trucksView on Amazon

These tools fit any vehicle. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.

After it starts

Drive for 20 to 30 minutes so the alternator puts some charge back, and ideally put the battery on a charger overnight. A jump start does not fix anything: it gets you moving so you can find out whether the battery, the alternator, or a drain is the actual problem. See signs your car battery is dying and how to test it with a multimeter.

If it needs replacing

Batteries are sized by group number and cold cranking amps, and the right one depends on the car. Look up the battery size for your year, make and model.

Frequently asked

Why does the last clamp go on bare metal instead of the negative terminal?

Connecting the final clamp completes the circuit, and that can spark. A lead-acid battery vents hydrogen while it charges and discharges, so the spark should happen away from it. Any unpainted bolt or bracket on the engine or chassis is a good ground.

Can you jump start a car with a portable jump pack?

Yes, and it is simpler: red clamp to the dead battery's positive, black clamp to bare metal on the engine or chassis (or to the negative terminal if the pack's manual says so), switch the pack on, start the car within the time the pack allows, then remove black first. Pick a pack rated for your engine size; large gas V8s and diesels need more peak amps than a four-cylinder.

Can I jump start a hybrid or an electric car?

Hybrids and EVs have a small 12-volt battery that can go flat like any other, and most can be jump started at a marked 12-volt jump point under the hood, not at the traction battery. Never use a hybrid or EV as the donor car: their 12-volt systems are not built to supply cranking current. Check the manual for the jump point.

The car started but died again. What now?

If it dies as soon as the clamps come off, the alternator is not charging and the car is running on the donor. If it starts fine but is dead again tomorrow, the battery is no longer holding a charge or something is draining it overnight. A battery over 4 years old that needed a jump is usually due for replacement.

Need your car's exact spec?

Find the right battery for your car if it will not hold a charge