Car Battery Dead? How to Jump Start Your Car Battery

jump-starting a car battery

It’s cold outside, baby. And you’ve just heard every driver’s nightmare—that clicking sound your starter makes just before your engine doesn’t start. For whatever reason (door left ajar, extreme cold, plain old dead battery, whatever) you will need to know how to jump start your car battery.

It’s a relatively simple procedure, but a few rules will make it safe and effective. Sure you can call a wrecker, maybe even one that’s covered by your auto club for free. Odds are it will take at least an hour for the driver to get there.  On the other hand, you could be back on the road in ten minutes if you simply do it yourself. I’ve done this in a three-piece suit and not even needed to wash my hands. With a little luck, you’ll still make the morning meeting—with enough time to enjoy a salted caramel latté to boot.

How to Jump Start Your Car Battery: Tools

  • Rule #1: have jumper cables. Have good ones. Light-duty (read: cheap) cables can save your bacon in a pinch, but will probably take longer to start your dead car. Inexpensive, thin-wired cables conduct less current, and may actually overheat and smoke if you’re forced to crank a flooded engine long enough to clear it out. Go big, or stay home.
  • Rule #1.5: have cables long enough to reach your battery. If you park head-in to a parking spot or driveway, the cables need to reach your battery and the donor car’s battery at the same time. 6-footers will only work if you can manage to maneuver the donor car nose-to-nose. I like cables at least 2-gauge heavy and 12 feet long. They can just live in your trunk. Odds are they’ll outlast your car, so don’t skimp.

Rest assured that you can not electrocute yourself jump-starting a car. The 12-14 volts in your car’s electrical system won’t give you a tingle even if you’re wearing wet shoes. The only exception would be the high-voltage battery in a hybrid or battery EV. And even then, you’d have to intentionally bypass a half-dozen interlocks and ignore several warning placards to get anywhere near the high voltage. Of course, you won’t be jumping that battery EV, will you?

How to Jump Start Your Car Battery: Step by Step Process 

1. Both Cars Should be Off & Identify the Jump Points

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Ready to jump start your car battery? Open both hoods. Shut off the donor car for now. Even if your car has a trunk-mounted battery, the jump point under-hood will be clearly labeled and colored bright red.

2. Connecting the Red Clamps

Connect one red clamp to the dead car’s positive terminal. This will be clearly marked + (duh), and probably has a red insulating cover. Keep the other red clamp off the ground, and away from anything metal, or you’ll get welding lesson.  Get a good grip with the clamp. If the battery terminal is loose or covered with fur, you may as well clean it up with some hot water and baking soda, and tighten the clamp (By the way, that’s probably why you’re jumping this car, as the connections to the battery weren’t good enough to let it charge fully). Now connect the other red clamp to the positive terminal on the donor car. It’s also red, remember?

jump start car battery


3. Connecting the Black Clamps (warning included)

Connect the black clamp to the negative terminal on the donor car. Again, you need a solid grip, which may not be easy with some cheaper cables. Now make the final ground connection. Warning! To avoid any sparks that could ignite any lingering hydrogen gas that the battery may have generated, you’re going to make that final connection to a ground point on the engine, not on the battery post. An alternator bracket, the corner of the cylinder head, even the cast aluminum intake manifold will be fine. Why is this important? A small explosion of hydrogen can blow the top clean off a battery, scattering battery acid all over the engine bay, the paint on your fenders, your clothes and into your eyes. (Just ask my old-time mechanic pal, Squinty, how battery acid feels when it gets in your eyes…)

4. Pause

All four connections made? Time to fire up the dead car and bug out, right? Wrong. I know it’s cold, and you’re late for work, but chill. Let the donor car’s battery charge your dead battery for a couple of minutes. Then start the donor car and let it idle for five minutes or so (lights and a/c off to reduce electrical load) to put some more charge into the dead battery. This procedure will also reduce the possibility of an electrical surge frying the delicate electronic computers on board.

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5 minute pause…

5. Starting Up

Okay, if your battery is only a little bit dead (the starter motor turns over, just not quite fast enough to start), you may be able to get it teased into life without out this pause that refreshes. The battery in the donor car may add enough oomph for ignition and liftoff. But if you’ve got a buzzing or clicking instead, your battery is seriously discharged. Wait a few minutes and let it recover a little.

Okay, now twist the key on your dead car. If the motor doesn’t start instantly, be patient. If the starter doesn’t spin briskly, give things another 5-10 minutes to charge with the donor car idling. Raising the donor’s engine speed above idle will help, and besides you get to spend ten minutes inside a nice warm car after stamping around out in the cold hooking up cables, and what’s wrong with that? Just remember to turn off as many electrical accessories as possible.

Dead car finally started? You just learned how to jump start your car battery, congrats!

Now remove the cables in the reverse order, close the hoods and go. Your alternator may take quite some time to recharge a fully-dead battery. If the car has been dead for some time, the battery may be so dead that it takes many hours before it even starts to take a charge. To be safe, charge the battery with ground-powered battery charger overnight to bring it up to full snuff. And unless you have a pretty good idea why your car wouldn’t start (like the dome lights being left on for a week or something like that), have a mechanic give your electrical system a checkout, including a battery load-capacity test. A single instance of deep discharge can reduce the lifespan of a battery by 25% or more, so please try to avoid getting into this situation.

Mike Allen-  guest writer for the Openbay blog. He’s an ASE-certified mechanic, longtime former editor of Popular Mechanics, and world-record-holding race-car driver. For more on Mike, check out his bio here, and find him on his own site, Saturday Mechanic.