/jump-start-car
How to jump start a car without damaging it
Short answer: connect positive to positive, then negative on the good battery to a bare metal ground on the dead car — never negative to negative on the dead battery. Start the good car, wait two minutes, then start the dead one.
Before you touch anything
- Both cars off, both in park (or neutral with the brake set).
- Batteries are the same voltage (12V unless you know otherwise).
- No leaking, cracked, or frozen battery. If the case is bulged or smells like rotten
eggs, stop — that battery can rupture.
- Remove rings and metal watch bands. A short across a battery terminal gets hot enough
to weld metal to your hand.
The cable order (this part matters)
- Red clamp → positive (+) terminal of the dead battery.
- Red clamp (other end) → positive (+) terminal of the good battery.
- Black clamp → negative (−) terminal of the good battery.
- Black clamp (other end) → bare metal on the dead car: an engine bracket,
a bolt on the chassis, away from the battery. Not the negative terminal.
That last step is the one people get wrong. Connecting negative to negative at the dead battery can create a spark right next to hydrogen gas venting from the battery.
Starting sequence
- Start the good car and let it idle for 2–3 minutes.
- Start the dead car. If it does not catch in about 5 seconds, stop and wait a minute.
Cranking repeatedly overheats the starter.
- Once running, remove the cables in reverse order: ground first, then negative
on the good car, then positive, then positive.
- Drive the revived car for at least 20–30 minutes, ideally on the highway. Idling in
the driveway does not recharge a flat battery well.
What the sound tells you
| Symptom | Likely cause |
|---|---|
| Rapid clicking | Not enough current — battery or poor connection |
| Slow crank, then starts | Battery on its way out, or a weak alternator |
| Cranks fine, never fires | Fuel or ignition problem, not the battery |
| Everything dead, no lights | Battery, main fuse, or terminal corrosion |
No second car? Two options
- Jump pack (lithium booster): $60–150, fits in a glovebox, safer than cables for
most people. Charge it twice a year.
- Roadside assistance: often included with insurance or a credit card. Check before
paying for a tow.
After it starts
The battery is not fixed — it is just charged. Get it tested (free at most parts stores). A battery that needed a jump will usually need another one within weeks, and the cause is often a failing battery, a weak alternator, or a parasitic drain.
FAQ
Can I jump start a car with a dead battery and a hybrid? Follow the owner's manual. Many hybrids have a specific jump point and should not be used as the donor car. EVs generally cannot be jump started in the traditional sense.
Does the engine need to run while jumping? Yes for the donor car, so its alternator keeps supplying current.
Why did my radio and clock reset? Normal after a full discharge. Some cars need a code for the radio — check the manual.
Last reviewed: November 2026. General information. Follow your owner's manual and wear eye protection.