What Happens When You Connect The Battery Terminals Wrong?

Jump-starting a vehicle or installing a new battery appears to be a simple process. You must clamp the connectors and transfer the charge from the working battery to the dead or low-voltage battery.

Automotive batteries produce electrical currents to start a vehicle. In any event, jump-starting the battery is a tried solution that you might consider if you cannot start your car.

Connect The Battery Terminals Wrong

However, what happens when you connect the battery terminals wrong? Will this damage the engine? How dangerous is it? We will answer these questions in this article, so continue to scroll up and read.

How dangerous is the incorrect connection of jumper cables?

Switching the connection of the battery terminals can seriously harm the battery, the vehicle’s electrical parts, and even the person doing it. It will result in a massive power surge and tremendous heat.

The system or its components won’t tolerate it well, and the damage will most likely be severe and irreparable depending on several conditions.

The dangers associated with incorrectly hooking up jumper cables or battery chargers can cause a lot of damage, or even result in an exploding battery.


Reversing battery cables is so dangerous that it can cause personal injury. Since car batteries vent flammable hydrogen gas, it can create sparks that can ignite the gas and result to:

  1. Fire
  2. Melted jumper cables
  3. Explosion
  4. Vaporized cable clips
  5. Injury

What happens when you connect the battery terminals wrong?

When the car battery terminals are connected in reverse it may result to loud sparks and smoke. The car's electric systems would have experienced a reverse electric current flow. Following this, the car will go entirely dead, be impossible to start, and have all of its lights go out and even cause fire or explosion.

While the lights are not in danger, you should be concerned about electronic devices that use diodes, such as the engine control unit. Significant damage will occur to the fuse’s components, followed by the fuse itself blowing.

The harm can end up irreparable, and you would have to work quite hard to make things right now.

Here’s what happens when you connect the battery terminals wrong:

  1. Fried electrical components
  2. Dead battery
  3. Melted jumper cables
  4. Blown fuses
  5. Damage wirings
  6. Personal injury
  7. Burnt chassis/hood

How will the incorrect connection of the battery terminals affect the battery?

There will be a significant electrical current surge between the two batteries if the positive terminals of each battery are connected to the negative terminal of the other battery. As a result, the batteries will heat up very quickly.

In the case of lead-acid batteries, the most prevalent type, a significant amount of hydrogen gas will be produced inside the charged battery. The pressure from hydrogen gas can cause the battery shell to shatter.

Photo from DW Akademie

Still, the heat can melt internal and external battery components. When the shell is broken, hydrogen that has escaped could potentially spark and explode.

Is it possible to become electrocuted when connecting the battery terminals? 

No. The current from the 12VDC system isn’t strong enough to hurt you. It may be difficult to recognize such low voltages because the current must overcome resistance to pass through.

The battery current must pass through your skin for you to be electrocuted or otherwise affected. High voltage current sources are not hazardous on their own.

Still, a few other things to watch out for when working with your car battery are acid leak, spark plug arcing, and jumper wires.

How to properly connect the battery terminals?

On a car battery, both positive and negative terminals are present. The color of each terminal and the symbol it displays serve as identifiers.

Photo from Insider

It is crucial to properly connect each terminal because a weak connection can obstruct the process and render the battery ineffectively charged. Now that the fundamentals are out let’s move on to the crucial issue.

Caution: You must exercise extreme caution and pay some level of attention.
  1. The positive terminal is always attached first in circuits to prevent a high voltage drop across the semiconductors. 
  2. Clamp the jumper cables to the battery’s positive terminal first, which is typically red and marked with a positive (+) sign.
  3. Only after these cables are securely connected should you start connecting the cables from the negative terminal, typically represented in black with a minus (-) sign.
  4. A metal object contacting the battery’s terminals should also be avoided.
  5. When the negative terminal is connected first and not the positive terminal, the entire chassis, including the metal bolts holding it, becomes grounded.
  6. On the other hand, it is suggested that when detaching the cables, you start with the negative terminal.


It’s crucial to pay attention to the terminals when connecting the car battery to prevent battery damage. This is due to the possibility that, like any other electrical component, a reversed connection could harm the car.

You can potentially suffer harm as a result of the process, and the battery will also be destroyed. We hope this article helps you understand what will happen if the jumper cables are connected incorrectly and how dangerous it is.

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