Car Battery Is Hot (6 Reasons + Solutions)

Keeping in mind that temperatures under the hood can get over 200 degrees F because of the engine running, it is understandable to have a warm battery. 

The keyword in this case is warm and not hot. When you notice the battery is hot, then there is an issue with it. 

Another reason for concern is when the battery smells and is swollen. It is vital to take the necessary steps and find a solution. 

6 Reasons the Car Battery is Hot

Many things would easily make the car battery overheat. We look at them below together with their respective solutions. 

1. You have a defective voltage regulator or alternator 

The alternator is key in charging the battery as you drive the car. Thus the reason it will always be full. 

The alternator can have a fault whereby it is charging the battery with too much voltage. This is what would make the battery heat up. 

The voltage regulator is also part of the circuit that recharges the car battery. Now, when it is faulty, it means there is no consistent voltage flow to the battery. That is how the alternator may overcharge the car battery. 

If you notice a hot battery, consult with a mechanic to check these two components to see which one has the issue. 

The solution is to simply replace the faulty alternator, voltage regulator, or both.

Here is how the voltage regulator works

2. The battery is failing 

If a battery is failing, the alternator needs to work a lot harder to ensure it is fully charged. As we know, constant charging of a battery would lead to more heat build-up. 

To make it worse, the battery is close to the engine which is operating at a higher temperature. 

You may notice that the battery light turns on more often. When you see the battery light on the dashboard, have the battery changed as soon as possible. 

Keep in mind that if you keep overheating the battery, it can easily swell and explode. That is not a good idea for a compartment with other sensitive parts. 

Make sure to have the battery tested first just to be sure it is failing. Then, replace it with a new battery for better operation and safety. 

3. There is a short circuit 

A battery can get hot because of an internal or external short circuit. 

In the case of an internal short circuit, it means that two plates in the flooded battery have touched each other. This will leave you with an overheated cell. 

Nowadays, more people go for AGM batteries. Such batteries are resistant to such types of damage. So, the chance of having an internal short is minimized. 

You do not want to be driving around with a shorted battery. The chances of it exploding are quite high. 

The external short occurs when the terminals of the battery touch each other probably through a piece of metal running from one terminal to the other. 

A good example is when you are working on something under the hood and accidentally place the spanner across the battery short-circuiting it. 

An external short is just as dangerous. So, try to avoid it as much as possible. You can have the terminals covered when working under the hood. 

Here is a video that shows how to test for a circuit in a battery:

4. Using the wrong charger 

Using the right charger can avoid overheating the battery. Make sure that you use the recommended type of charger specific to your battery. 

Also, you cannot use a charger meant for flooded cell batteries on AGM and gel batteries. Always ensure you consult the shop attendant to get you the correct charger. 

AGM batteries generally discharge slowly thus the need to charge them in a similar manner. 

Luckily, newer battery chargers have the option of choosing the correct charge mode depending on the battery type. So, you can have a single charger for various models. But stick to the recommended charge mode for a battery type.

Also, do not overcharge the battery unnecessarily. Once the battery is full, simply disconnect it from the charger. 

5. Loose battery connection 

A loose connection on the battery terminal leads to increased resistance. That is how the battery ends up heating. 

In case you had disconnected the battery terminals, ensure they are tightened back correctly before closing the hood. 

Consider checking for signs of corrosion build-up on the terminals too. The build-up would also make the battery have a poor connection with the cables going to it. 

6. Using the wrong battery cable grade 

You cannot just buy any cable and use it for transmitting power to and from the battery. 

People make this mistake and use poor quality or wrong grade of cables for battery connectivity. As a result, you end up with low performance or increased resistance thus creating heat that is dispatched by the battery. 

Look at the car power requirements and use proper cables to avoid overheating and potentially melting the cables onto the battery terminals. 

FAQs

How long does the car battery last?

Most car batteries last up to 5 years and then you have to replace them. A visual check or battery test can help know when to change one. 

How do you tell the car battery is overheating?

Other than the battery being hot, it will give off a rotten egg-like smell. This is mostly for the flooded battery. The smell is because of mixing water and sulphuric acid. 

Can engine heat make the battery overheat?

When the engine keeps overheating, then it is possible for it to affect the temperature of your battery too. But in this case, the battery cools down easily after a few minutes not as compared to when maybe you have an internal short. 

Can hot weather make the battery hot?

This is a more of hot to touch kind of scenario. However, some very high temperatures can cause the voltage regulator to malfunction thus overcharging the battery. 

How can you prolong the battery life in your car?

Perform regular cleaning to ensure the battery is in good working condition. Also, invest in the right charger to have the battery charged correctly. In case it is a flooded battery, ensure its fluids are topped off correctly.