Why your Car battery is Overheating? (+ What to Do)

Note: The information provided here is intended as a guide. Always consult a qualified auto mechanic

Wondering why your car battery gets extremely hot? Sometimes a car battery can get really hot and even give off a strong, bad smell.

In this post, you’ll find possible reasons why the car battery may overheat, early signs to look out for to alert you of an overheating battery, and what you can possibly do to fix an overheating battery issue.

What Causes a Car Battery to Overheat

If a car battery is overheating then it might be because:

#1. The battery is damaged. The car battery itself may be damaged and have an internal short in one or more of the cells.

This results in a higher current draw than the battery is designed for which increases the battery temperature.

#2. The car engine bay is extremely hot. This may be because of an overheating engine. Is the car engine radiator damaged and leaking coolant? If so, then this causes the car engine to overheat and heat up the car battery too.

Why Does My Charger Get Hot? -
Why Does My Charger Get Hot? -

#3. Faulty alternator. A faulty car alternator with a bad regulator can subject the battery to higher than recommended charging voltages.

Signs a Car Battery is Overheating

An overheating battery will get extremely hot to the touch such that you cannot keep your hand on it without causing injury. It may also:

  • give a strong, rotten egg-like smell, hydrogen sulfide gas.
  • hiss or sizzle sound
  • bulge at the sides.
  • The battery voltage reading may be in excess of 14.5V

Additionally, you may also go through several headlight bulb replacements as each set burns out quickly from the alternator overvoltage.

Battery Overheating – What to Do

If the battery is overheating, as a first step, open the hood with the car engine off and let the battery or engine cool to normal temperatures.

#1. Check if the car engine overheating. Does the dashboard display a temperature warning? Perhaps it is a damaged or leaking radiator, i.e. a failure in its cooling system that caused the battery to overheat.

Does the car have coolant in the reservoir? Other possible causes (depending on the car model) may be a broken alternator that keeps the engine cool by driving the water pump and fan to prevent overheating of the engine.

Have the car inspected by a qualified mechanic and get the car’s cooling system fixed.

# 2. Once the car battery has cooled down, you can measure the battery voltage while the engine is running. The car battery voltage will normally be in the range of 13.5 -14.5V when the engine is running.

Is it considerably higher? If so, you probably have a faulty alternator (with a malfunctioning voltage regulator) that needs to be replaced.

#3. You can also measure the battery voltage when it is disconnected from the alternator. If the voltage reading is sub 12V, for example in the range of 10.4 -10.7V then the car battery may have an internal short.

Have it tested at an auto parts store. If damaged, replace it. You may also be interested in this post: Sings that a car battery may be shorting (+ How to confirm)

How Hot Should a Car Battery Get?

It is normal for the battery temperature to increase during the charging process depending on how much current the alternator pumps into the battery. Some batteries are able to handle high temperatures better than others.

While each battery has a recommended limit temperature beyond which its performance degrades and it becomes a safety hazard, it is best that the temperature is warm to the touch to avoid damage.

The Dangers of Overheating Car Batteries

Excessive heat can damage the battery permanently, requiring an investment in a new battery.

Beyond the possible investment, an overheating battery, can bulge and spew acid from the temperature buildup. This is a safety hazard and can cause severe and permanent injury.

Closing Thoughts

Excessive temperature buildup of the battery can be caused by a faulty battery, alternator, or overheating of the car engine.

If the car battery is extremely hot, switch off the engine and allow it to cool as it can explode and cause severe damage and injury.

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