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How To Boost A Car Battery

Posted By Tipnut On February 12, 2007 @ 7:22 am In Fixes & How-To | 42 Comments

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.


  • 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.


  • 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.


*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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