A jump start is enough if the battery went flat for a clear reason: lights left on, a door left ajar, the car sitting for weeks. You probably need a new battery if it's more than three to five years old, if it keeps dying, if it struggles even after a long drive, or if it's swollen, leaking or corroded. A battery and charging test settles it in minutes.
When a jump is probably all you need
- You left the headlights, dome light or a charger plugged in overnight
- The car sat unused for several weeks
- The battery is fairly new and has never given trouble
- After the jump, the car starts normally again the next day
Drive for at least 20 to 30 minutes after a jump so the alternator can put some charge back.
Signs the battery needs replacing
- Age: three to five years is typical; heat shortens it
- It keeps dying even when nothing was left on
- Slow cranking most mornings, worse in cold weather
- Swelling, cracks, leaks or heavy corrosion at the terminals
- A rotten-egg smell near the battery
- A load test fails: the battery can't hold voltage under the heavy draw of starting
If a battery dies repeatedly, the problem may not be the battery at all. A failing alternator or a part that drains power with the car off can do it. See bad battery or bad alternator?
How to jump start a car safely
Park the good car close, both engines off, parking brakes on.
Connect red to the dead battery's positive (+) terminal.
Connect the other red to the good battery's positive (+).
Connect black to the good battery's negative (−).
Connect the last black to a bare metal point on the dead car's engine, away from the battery. Not the dead battery's negative terminal.
Start the good car, wait a few minutes, then try the dead one.
Remove the cables in reverse order.
Check your owner's manual first. Some cars have specific jump points under the hood, especially if the battery is in the trunk or under a seat.
Don't jump a battery that's cracked, leaking or frozen.
If the jump doesn't work
Rapid clicking that continues with cables attached can mean a very dead battery or poor cable contact. A single click may point to the starter instead. Our guide to car clicks but won't start explains both.
Mobile battery replacement
A mobile mechanic can test the battery and alternator, bring the right battery for your car and install it where the car sits, often in well under an hour. Some newer cars also need the battery registered with the car's computer after it's replaced, which a mechanic's scan tool handles. More in mobile battery replacement.
Frequently asked questions
How many times can you jump a battery?
There's no fixed number, but needing jumps regularly means something is wrong. Get it tested.
Can a jump damage my car?
Done correctly, rarely. Connecting the cables in the wrong order or to the wrong points can damage electronics.
Are portable jump starters worth it?
For many drivers, yes. A charged pack in the trunk means you don't need a second car.
Get the battery tested
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