Hooked battery up backwards now car won’t start- How to Fix it?

As vehicle owners, you may need a battery replacement for several reasons. While replacing it, you mistakenly hooked up the battery backwards. Don’t panic; you are not alone. It is a common mistake that can happen to even the most experienced car owners. But what now? Your car won’t start, and you are left scratching your head. “hooked battery up backwards now car won’t start” Check the solution below.

Check for the fusible link or mega fuse, test for continuity and voltage with a multimeter. Replace the fuse if necessary. If a problem exists, check the battery with a multimeter. Replace the battery if it is damaged.

I will explore the risks and how to fix the hooked-up battery backwards. So, let’s dive in and get your car back up and running.

Can you ruin a battery by hooking it up backwards?

Can you ruin a battery by hooking it up backwards?

Yes, a battery can be ruined if it is hooked up backwards. When a battery is connected in reverse, the positive and negative terminals are switched, which can cause a short circuit.

A short circuit can generate a large current flow in the opposite direction, damaging the battery’s internal components. You may damage the electrolyte or the plates.

Furthermore, some batteries may release toxic or corrosive materials if damaged. Therefore, it is essential to always connect a battery correctly to avoid any potential damage or hazards.

What happens if a battery is hooked up backwards?

A battery hooked up backwards can lead to several risks. It may damage electronic components, circuits, and the battery itself. Here are some possible dangers that can occur.

Damage to the Charger’s Electronic Components

The current going to the battery can damage the charger’s electronic components. It may lead to a complete breakdown or damage to a part of the circuit.

Ruined Circuit

The charger’s circuitry can be ruined in part or entirely due to the reversed polarity.

Overloading Circuit

If the charger’s rating is lower than the battery’s capacity, the circuit may overload. You may experience tripping the circuit breaker and stopping the operation of the circuit.

Overheating and Burning Battery

If the charger’s rating exceeds the battery’s capacity, it can cause it to overheat and burn with ejection.

Irreparable Harm or Spark Discharge

The battery may be irreparably harmed or spark discharge due to reversed polarity.

Acid Damage

A damaged cover on the battery allows acid to enter. It can melt delicate equipment and potentially cause serious issues if it happens.

What are the signs that I hooked up the battery backward?

Here are some major signs that you may experience if you hook up a battery backward.

No power or response

If the device does not power on or respond when you try to use it. It can be a sign that the battery was hooked up backwards.

Smoke or burning smell

Smoke or a burning smell is also a possible sign of a hooked-up battery backwards. If you see smoke or smell of burning coming from the device or battery, immediately disconnect the battery and inspect for damage.  It can save you from severe damage.

Reverse polarity protection

Some devices have reverse polarity protection built in and will not power on if the battery is connected backwards. However, not all devices have this protection. So it is essential to double-check the polarity before connecting the battery.


If the battery or device becomes excessively hot or bulges, it may be a sign that it was hooked up backwards.

Damage to the battery or device

Physical damage to the battery or device is also possible. You can experience instances such as melted plastic or burn marks.

How to fix- Hooked battery up backwards and car won’t start? [Step by Step Guide]

How to fix- Hooked battery up backwards and car won’t start? [Step by Step Guide]

Fixing the hooked-up battery backward is simple if you follow the steps below.

Most modern-day cars have a fusible link or mega fuse on the positive side of the battery cable. Check if your vehicle has one and test it for continuity or voltage with a multimeter. I recommend the Klein Tool multimeter. It is affordable and simple to operate.

Step 2: Test for Continuity

Set your multimeter to “continuity” and connect one side of the fuse. If there is no beep or continuity, it means the fuse is bad.

Step 3: Test for Voltage

Then, set your multimeter to read the DC voltage and check the voltage on the front and back sides of the fuse. The fuse is bad if there is voltage on the front side but not on the backside.

Step 4: Replace the Fuse

Now you have confirmed that the fuse is bad and needs replacement. Disconnect the negative battery cable and remove the nuts on both sides of the fuse with a 15mm socket. Replace the old damaged fuse with a new one, which may cost around $5.

Step 5: Reconnect the Battery

Cover the fuse and reconnect the negative battery cable. Start the car to make sure it works.

Step 6- Test the battery

If you have left the battery for a longer period of time, there is a risk your battery may be damaged. If the vehicle is still not starting, check the battery. Connect the multimeter to the battery terminals and read the voltage on the LCD. If the voltage is less than 12 volts, you may have a problem with the battery.

Step 7- Charge the battery

Remove the battery, connect it to the charging source, and leave it for at least an hour.

Step 8- Recheck the batter

Again, check the battery voltage by connecting it to the multimeter. If it is okay, mount it; otherwise, you need a battery replacement. You have many choices for 12V batteries. But my recommendation is the XS Power D3400R 12V Battery. It is not only affordable but also performs excellently and is long-lasting.

Step 9- Install new battery

Install a new battery in place of the old one. Make sure all the connectors and wires are correctly connected.

Step 10- Test the car

Finally, test the car and ensure everything is working fine. Once it is done, remember and be careful in the future if it happens again.

Can I start a car with a hooked battery up backward?

Can I start a car with a hooked battery up backwards?

No, you shouldn’t try to start a car with the battery hooked up incorrectly. When the battery is connected incorrectly, it can cause a spark. It has the ability to ignite the battery’s explosive gases. Furthermore, it can damage the car’s electrical system, such as the alternator, starter, and other sensitive electronics.


How much time does it take to fix a hooked battery up backward?

Fixing a hooked battery up backward can cause severe damage to the vehicle’s electrical system. The time it takes to fix this depends on the extent of the damage caused. It can take anywhere from a few minutes to a few hours, depending on the problems.

How much is to fix a hooked battery up backward?

Fixing a battery hooked up backward can cost anywhere from a few hundred to several thousand dollars, depending on the extent of the damage caused. It can damage the car’s electrical system, components, and engine, leading to expensive repairs or replacements.

Can I fix a hooked battery up backward myself?

Yes, you can fix a hooked battery up backward yourself, but only if you have the knowledge and experience to do so safely. Otherwise, it is recommended to seek professional help to avoid potentially dangerous consequences.

Is it safe to drive my car after hooking up the battery backward? No, it is not safe to drive your car after hooking up the battery backward. Reversing the polarity can damage the car’s electrical system, including the alternator, starter motor, and other components. It is best to have a mechanic inspect the vehicle before driving it.