How To Boost A Car Battery

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Here are step-by-step instructions for how to boost a “dead” vehicle, feel free to print them out, put in a plastic sleeve and tuck into your car’s glove compartment.

ExampleFirst:

  • You’ll need someone with a running automobile to give a boost plus a set of jumper cables.
  • You can either turn off the running auto before attaching the cables, or leave it running. Your choice.

Admin Edit – Correction Made From the comments area below:

Connecting the black (ground) jumper cable (of dead negative grounded vehicles) to the sheet metal of the vehicle rather than the negative terminal is a very important safety feature.

Batteries can and do emit gas and if you get a spark while connecting the cable to the negative terminal the close proximity to the gas can result in a battery exploding in your face. Generally, you only make this mistake once.

Directions

  • Pull the running vehicle up close to the one that won’t start. This can either be side-by-side or hood to hood. Just make sure they are close enough for the cables to reach both.
  • Take out the cables and make sure to never touch the ends to each other at any time.
  • First work with the running vehicle. Take one end of the cables and attach them to the battery which is usually up front near the corner of the car when the hood is popped up.
  • There are always two posts on a battery, one is positive and the other is negative. The positive post is usually bigger than the negative, has more wires going to it, is frequently colored red and has a + sign beside the post. *See Pictures Below
  • Working with the same end of the booster cable (one red clamp and one black clamp):
  • Clamp the red end of the cable to the positive post.
  • Next clamp the black end of the cable to the negative post.
  • Now you should have both clamps from one end of the cables attached to the battery of the ‘working’ car.

Very Important: Make sure to NEVER let the clamps of the cables on the loose end touch each other or you will have flurry of sparks.

  • Working with the ‘dead’ car and the other end of the cables, follow the exact same procedure above. First attach the red positive clamp to the positive post, and the black negative clamp attach to a grounded piece of sheet metal of the vehicle (read comments below).

Important: Make sure to attach the red positive clamp first, then the black negative clamp.

  • Now both ends of the cables should be attached, one end to each automobile. Red clamps attached to each positive post, and black clamps attached to the negative post on the running auto and the other negative clamp attached to a grounded metal part of the other vehicle.
  • First turn on the ‘working’ vehicle. Then try starting the ‘dead’ auto. If it doesn’t start right away, you may need to let the running vehicle run for a minute or two to charge it, then try starting the dead auto again.
  • If the dead car still doesn’t start, make sure the clamps are on the posts properly and have not fallen off.
  • Once the “dead” vehicle is running, do not shut it off. Keep it running so it recharges.
  • Remove the cables from one automobile at a time.

Important: First remove the black negative clamp, then the red positive clamp.

  • Hold the detached clamps in one hand away from the other end while removing the second cable end from the second automobile–or sparks galore again.
  • Once the cable has been removed from both autos, it’s safe to wind them up and put them away.

Pictures

*Note changes made, the negative clamp on the dead battery should be on grounded metal instead of on the negative post.

Looking from behind, here is a picture with the posts on the side, the positive post has a red cap that first needs to be lifted off. You see the negative (black) post on the right, no cap, and looks just like a nut and bolt. That bolt is where you clamp the cables to:

Image 1

Here is a view looking from the front of the hood, you’ll notice the top of the red cap hanging off and the clamps from the cable are attached to each post:

Image 2

Here is a picture of an older model, the posts are on top, uncapped and quite a bit larger to work with (instead of just a nut/bolt). You would clamp the cable onto each circle of the metal post. You can see the post on the right is tagged red (positive) and is a little larger than the negative post on the left:

Image 3

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Published: February 12, 2007

What Readers Are Saying:
42 Comments to “How To Boost A Car Battery”
  1. Mike says:

    Great post, but a couple of tips I have learned over years of driving “beaters” in the north.
    When connecting the clamps to the batteries start with the dead car and attach only the positive lead, let the negative clamp dangle or set it on some plastic. Then attach the positive lead on the good car, then the negative on the good car. This way you have not exposed yourself to any potential voltage because you have never handled a live positive and a ground at the same time. Now you can connect the ground on the dead car, but not necessarily to the battery post, any bare metal (no paint) will do. Find a spot that is not going to have any chance of contacting the positive and has no flammable materials near it. When you make this connection watch for a spark, if there is none check all your connections and try again. Removal would be reverse of application.

    Oh, and if you wonder what the difference between the $10 cables and the $40 cables is:
    $10 cable = charge for 5 minutes then start
    $40 cables = start car immediately
    cheap cables can’t pass the full power to start a car so a little patience or $ will save time

    Also smaller running cars to larger dead cars, especially trucks I have noticed the small car might need a little throttle, just over idle, to generate enough power to run the larger starter motor.

    • Shirley SELLERY says:

      That is great tip you gave them. You gave the consumers a very clear view of what they are getting if they use cheaply made products. But it seems a lot of importers are pushing lousy cheaply made products to the consumers…

  2. TipNut says:

    Wow, fantastic info there Mike, thank you :)!!

  3. tara says:

    Question: If you want to charge a bad batter with a good one from another car can you just hook up the jumper cables and leave them for a while or do the cars need to be running? Thanks!

  4. TipNut says:

    I’m pretty sure they have to be running Tara.

  5. ┘ŹSaleh says:

    Thank you very much Mike , Really I need these Information for a research in my homework ^_^

    thanx !

    • Equorial de Costa Rica says:

      Actually Tara, if you connect a dead battery to a fully charged one (without the engine running on either vehicle, the dead battery will “steal” the electrical charge from the good battery until both of them are ‘more or less’ equal in “potential voltage.” In short, you will discharge the good battery to the point of, let’s say, both batteries having about the same amount of “juice” inside of them. SO! This being said, it may take extra cabling to start either car because BOTH batteries might have to be hooked up via cables so that they performed as if they were “one” …therewith giving enough energy to start the vehicle. It is for this reason that it is usually best to leave the “good” battery’s alternator ‘turning’ (meaning that you should leave the car with the good battery running …although I don’t practice what I preach unless the dead battery obviously needs to be charged a tad using my alternator as an energy source, (through my battery and subsequent charging cables (or booster cables, your choice of words there). Cheers! :-)

  6. Jay says:

    “Question: If you want to charge a bad batter with a good one from another car can you just hook up the jumper cables and leave them for a while or do the cars need to be running? Thanks!”

    Well it’s relative really. You can charge a battery with another car if this car is running but it’ll take time and probably won’t get to the maximum charge.

    When you have batteries set up in both car, you don’t have to start your car in order to charge the battery but sometime you do when the battery is very low or it needs a lot of power! Usually we start the car in order to give a boost! :)

    The reason we run the car with a low battery it’s because the alternator(electronic device) make your battery charge as long as your car is on.

  7. Jay says:

    What we should do instead of leaving our car on while giving a boost is to stop it before! Let your car charge the battery from the other vehicule (about 5-10 minutes) then stop your engine!

    Here’s the short and sweet explanation: the alternator on the running vehicle will produce maximum electrical output when the other vehicule have a hard time to start! This means that you can damaged your alternator.

    By doing this you save yourself over 100$ and you just made someone happy!

  8. john says:

    these directions are wrong you dont connect the black cord to the negative on the dead batter you connect it to a metal ground like a bolt or something

    • Omar says:

      You have poor reading comprehension. The directions do not say to connect to the negative on the dead battery.

      “black clamps attached to the negative post on the RUNNING auto and the other negative clamp attached to a GROUNDED METAL PART part of the other vehicle”

  9. TipNut says:

    John the directions aren’t wrong, you hook the negative clamp on the negative battery post. Doing it your way is another option.

    • BSB says:

      Just a thought here but I was always told that you should connect either TO or as close to the battery terminals as possible to AVOID the chance that not all bolts or metalwork is truly grounded.

      This is more important on todays cars where many composite materials are used and even some mountings are not as conductive to electrical currents as people think.

  10. Myke says:

    Dont tell your mechanic about your booster cables, one kept mine, so i have no clue who in the last year it was. LoL.

    The main thing to remember is POSITIVE + first.

  11. Allan W. Greeley says:

    Connecting the black (ground) jumper cable(of dead negative grounded vehicles )to the sheet metal of the vehicle rather than the negative terminal of the dead battery is a very important safety feature. Batteries can and do emit gas and if you get a spark while connecting the cable to the negative terminal of the battery the close proximity to the gas can result in a battery exploding in your face. Generally, you only make this mistake once.

  12. TipNut says:

    Allan thank you for that info, after all these years living in “cold country” and all the battery boosting over the years, we’ve never known that. The original instructions were to a “T” what my husband was taught both in shop class and by his father.

    I’ve corrected the info above. Although the original instructions will boost a vehicle (and how Mr. Tipnut has boosted batteries for over 25 years with no incident), it’s best to be as safe as possible and take necessary precautions just in case.

    I can guarantee we’ll be boosting batteries the safer way from now on, thank you again :).

  13. sd says:

    Ok, I just came back from trying to start my dead mazda rx7 off my live durango. The rx7 has been sitting all winter..yes the battery was still connected, don’t ask. It didn’t want to start, lights worked, sounded like it was trying, checked all hookups. SHould I have been more patient, it usually starts right away in past.
    thx

  14. BrAdAsS says:

    If you both use an Absorbed Glass Mat style battery like a Deep Cycle Optima Blue Top then you don’t have to worry about hooking to the dead vehicles chassis, straight to the battery -.

    AGM batteries do not output the charging-reaction gas and are sealed.

  15. pbarc552 says:

    Here’s a tip for all you folks that have problems with boosting your car (with suspected starter problems):

    If you are able to receive a charge from someone who was nice enough to stop to help you but you notice that your starter is not engaging or the engine is simply not turning over you can try taking a crow bar or some other long thin heavy metal object to knock the starter while you have someone try turning the key on the ignition. The reason: OLDER VEHICLES (HIGH KM VEHICLES) SOMETIMES HAVE STARTERS WITH STUCK WORN BRUSHINGS. GENTLY KNOCKING THE STARTER WILL HELP MOVE THE STUCK STARTER’S MOTOR BRUSHINGS TO START THE CAR. I know this works because its happened to me.

    God Bless

  16. Brad says:

    Thank you so much! You saved me from much embarrassment when my girlfriend woke me up to help the cute neighbour boost her car. I was able to walk out and be the hero without either one of them being the wiser.

    Now I just hope my gf forgets how rude I was to her because she woke me up early when I’m on nights. Got an article for that? lol

  17. John M says:

    OK, I am dumb when it come sto cars. Mine has in the last two weeks, taken 3 tries before it starts, and runs not so smoothly. Not sure if it’s because the weather has been getting colder, but as of yesterday, the car would not start (really cold here now) and just hear clicking noises from engine area. The panel will light up, and I believe the window went down and defrost came on. Going to try a boost soon, but does this sound like it’s just battery???

  18. TipNut says:

    Hi John, this is what my husband said: He suggests taking your car to a mechanic and getting both the battery and the alternator tested (I don’t think this costs very much to get tested). It could be either your battery or your alternator (meaning the alternator is not charging the battery). If it’s the battery, it will take a boost and get you running for a bit, but will start dying off. Hope that helps, but this is something you’ll want to take care of asap before you get stranded (getting too cold for that!).

  19. John M says:

    Thanks for the info. A buddy of mine has suggested once the car is running after the boost, and the booster cables are off, to disconnect the positive side (red) of my battery, and if the car still runs, then it’s not the alternator. Does that sound right?

  20. TipNut says:

    Yes, hubby says that’s right. Good luck! [Edit To Add]: My husband isn’t a mechanic btw, he’s just really good with this mechanics stuff ;).

  21. Amanda says:

    Can’t you leave one car running and THEN hook up the jumper cables–this way we wouldn’t drain the “booster battery”.

  22. Bob says:

    Hi. My car battery was dead, and we tried boosting it with another car. But the car with the dead battery just doesnt start. There is currents going through the jumper cables to the dead battery, but the dead battery just wont start. Is there a problem somewhere else in the car?

  23. Richard Friese says:

    Be careful jump starting new model cars. If you jump start a car with a computer board, you can overload the computer chip and blow it, costing loads of $$$ to install and replace the board. Check the owners manual before you need to jump start a car. Many models have specific steps to hook up the cables. By reading the car manual before needing it, at least you will have some idea of how to jump start the car, when you need to take the manual out on a dark road or parking lot, to follow the jump start steps. RJF

  24. Cam Peneff says:

    Good instructions, but I don’t care for the picture where the two booster cable clamps are Very close together. While you are working it would be quite easy for them to slip and make contact. A better pic would show the positive clamp on the battery and the negtive on a ground. I personally prefer the alternator, although it’s not always handy (sometimes out of reach). Most vehicles these days don’t have any bare metal on the body, it’s all painted, and more and more bodies are going to plastics and other non-conductive composites.

    • Sparkadelic says:

      I agree 100% BAD picture, bad technique. Dont ever get the cables that close. A “dead” short could cause that battery to blow up in your face. You surely dont want battery acid in your face or all over the engine compartment.

  25. Shahid says:

    Can someone please give me the reason, while boosting a baatery from another vehicle, why it is important that both vehicle must not physically touch each other ?

  26. David says:

    Shahid says:
    Can someone please give me the reason, while boosting a baatery from another vehicle, why it is important that both vehicle must not physically touch each other ?

    Reply
    Vehicles should not touch because it can create a circuit between them.

  27. Jane says:

    After boosting the dead car, how long should you leave the car running to continue to charge it?

    • Jacob says:

      There are too many variations if it’s just the battery a minute is fine but if it’s the alternator that’s the problem you have to keep it running until you reach your destination, preferably the mechanic.

  28. alan says:

    Great info thanks.

  29. ahad says:

    hi guys what can happen if the jumper cable connect to the wrong connection ,i mean red to clack and black to red,because i did this things my car doesn’t get charge?

  30. rahul bhide says:

    One thing i have experienced. Using a $10 cable works perfectly fine for giving a ‘boost’ to the battery. I think you do not need to spend money on that buying a costly cable. Also the -ve (black end or ground) as mentioned earlies best can be found on heavy bolt/ nuts, avoid aluminium parts which are white/silvery color.

    Thanks a lot for this informative post. Boost to my battery just went well.

    • Sparkadelic says:

      Wrong, in my opinion. $10 cables are usually short, smaller gauge wires with flimsy/weak clamps. A more expensive set of cables are WAY better but not necessary. One of those situations that you truly do get what you pay for. If you only use them once a year the cheapys may be ok. I grew up on a farm and we boosted more things than I can remember. If you need to boost larger vehicles that require more cranking amps the cheap cables can get HOT, hot enough to start to melt the CHEAP insulation off. My father used welding cable and made his own with Quality clamps. They are still around and are with me 20+ years later. They would have been expensive to build and even more to buy but they are the best. Plenty long and durable.

  31. edward says:

    alot of good advice!!!question? does this boosting a vechile that is very new like 2009 this way have anything to do with maybe damaging or ruining the computer in either car if both are new. its been ages snice i have received or given anyone a boost TY

  32. Terry says:

    Hello, Can anyone confirm boosting today’s cars (200x) does not risk damage to the computers? I have heard rumos boosting could damage them. Thanks
    Is the special considerations (having the good car off etc)

  33. brittnae says:

    Hi, yesterday morning it was coooold and my boyfriend went to start his car and it wouldnt start so he kept trying but still didnt get it to start. So we called someone to jump our car and even that didnt help. ttodayyou can barely hear it try turning over. We dont know if its the battery or something else. Could yall give me advice on what it could be? Please and thank you

  34. Tim says:

    Vehicle batteries are sealed. Very slight chance of explosive vapors. Trying to find an actual grounding point on newer vehicles is vitually impossible. The chances of getting wires tangled, body dismemberment from fans and pulleys are more common than sealed batteries exploding. Cables that you buy today are garbage. Chances of them failing are greater than all other scenarios. For the cost of a decent set of cables, you could buy a nice booster pack… that not only starts your car, but pumps air to your tires, charges your phone, emergency light and signaling, etc…


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