Last updateMon, 16 Oct 2017 11am

On The Road

Use caution when you jump-start any vehicle

Q: After work the other day, I went out to my car and it would not start. One of my co-workers volunteered his car to jump-start mine. My car started, and I drove it to my repair shop. It turned out all I needed was a new battery, but my repair shop told me that jump-starting a car can be dangerous or can cause electrical problems if not done correctly. So, was I just lucky that nothing happened or are they exaggerating the possible concerns? And why did the battery go dead like that with no warning?

A: There are a number of things that can go wrong and cause serious damage to a vehicle’s electrical system or even harm you if the jump-start is not performed correctly – cables crossed, hooking a positive to a negative, etc.

As reliable as good batteries are, they will eventually wear out and may stop working with little or no warning. Even though a battery may not crank the engine over, if you can get the engine running with a jump-start, the vehicle charging system can supply enough power to keep it running and allow you to get to a repair facility.

Jump-starting is the process of connecting a dead battery to a fully charged battery. There are special cables – jumper cables – that will perform this function. The cables must be connected in a specific way to avoid damage to the electrical system of either vehicle and to prevent a battery explosion.

Yes, the battery can explode.

A battery vents explosive hydrogen gas, especially when discharged or dead and being jump-started. Hydrogen gas can explode if it comes in contact with an open flame or a spark. So, do not smoke while jump-starting a car. Also, be sure to remove any metallic chains or necklaces that could come in contact with the battery terminals.

Battery terminals are marked “+” (plus) and “–” (minus). The + (plus) terminal is usually marked with the color red in some way. To avoid hurting yourself or the car’s electrical system, the jumper cables must be connected correctly and in the proper sequence.

Before connecting the jumper cables, make sure that the battery is sealed and all caps are in place. Always start by connecting the positive cable first. Connect the cable from the positive battery post on the starting vehicle to the positive post of the battery on the stalled vehicle.

Next, connect one end of the negative jumper cable to the negative battery post of the starting vehicle battery. The other end of the negative jumper cable should be attached to the engine block or frame of the stalled vehicle.

Now, start the good vehicle. Once it is running, start the stalled vehicle. Once the stalled vehicle is running, disconnect the jumper cables in reverse order of how they were installed.

Why is connecting the jumper cables in this way so important? Reversing the cable connections such as positive on one battery to negative on the other battery could, and probably will, cause severe electrical damage to one or both vehicles. Connecting the negative jumper cables to both batteries, then connecting the positive jumper cables to both batteries, could cause a spark and then an explosion.

Jump-starting a stalled vehicle can be done safely if the correct procedures are followed. Otherwise, bad things can happen.

In the future, you may want to opt out of the jump-start and call a tow truck to transport your vehicle to a repair facility.


Warren McCord is an ASE Certified Master Technician and owner of Dean’s Automotive Inc., 2037 Old Middlefield Way, Mountain View. For more information, call 961-0302 or email McCord at This email address is being protected from spambots. You need JavaScript enabled to view it..

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