How the Summer Sun Can Hurt Your Car's Battery

Stephen Fogel
June 5, 2018

When your car won’t start, the battery is most often the culprit. And while many people think winter is the harshest season for batteries — all those freezing temperatures and ice storms can’t be good — summer is actually even more damaging.

Hot temperatures, both outside and under the hood, can harm your battery. Very often, the extent of this damage will not be obvious until you try to start your vehicle on a very cold winter day, a few months later. Then the winter weather unfairly gets the blame.

Let’s take a look the effects of hot weather on your battery, or you can skip ahead to learn how to minimize the damage these sizzling summer days can cause, and see the symptoms of a bad battery.

The effects of heat on your car battery

The outside temperature has a direct effect on your battery. The ideal operating temperature for your vehicle’s battery is around 77 degrees Fahrenheit. Good luck with that during the summer.

When it’s hot out, you have the heat produced by the engine, plus the sun’s heat absorbed by your hood, added to the heat reflected up from the road surface underneath. It all adds up to a bad environment that could end up with you needing a jump start or a tow.

Here’s how scorching temperatures can hurt your car battery:

Fluid evaporation: Intense heat can cause the fluid in your battery to evaporate. This results in reduced electrical output, less starting power and damage to the internal battery structure.

Internal corrosion: High temperatures inside your battery accelerate the corrosion process. This affects the lead plates inside it and the places where the cables connect to the terminals on the outside. Corrosion limits the power your battery can send out.

Battery overcharging: Your vehicle’s voltage regulator controls how fast the alternator recharges the battery while you drive. High heat can cause the voltage regulator to malfunction and overcharge it. Over time, this will damage and eventually kill your battery. 

» LEARN MORE: Get an estimate for a battery replacement

How to reduce the effects of heat on your battery

OK, so you can’t do anything about the temperature outside, but there are a few steps you can take to keep your battery healthy. 

Take cover

Do whatever you can to keep your vehicle cool when it’s hot outside. That means keeping it out of direct sunlight. Park it in a garage or under a carport if possible. Pick a spot in the shade when you have that option. Cover it with a light-colored car cover, especially if your vehicle is a dark color, which absorbs more of the sun’s heat.

Make sure your charging system is working

Your battery is just one part of your vehicle’s electrical system. Its charging system is responsible for recharging your battery and maintaining its ability to start and power your vehicle’s other systems. Remember, overcharging your battery is as bad for it as undercharging it.

This is why it’s important that your alternator, voltage regulator and other related components are all working properly. Have your mechanic check your charging system thoroughly.

Keep your battery clean

Corrosion and dirt can accumulate on top of the battery, particularly where the cables attach to the terminals. Both substances are bad, but in different ways. Corrosion acts as an insulator, reducing the flow of current. Dirt is a conductor, and drains your battery’s power.

To keep the top and case of your battery clean, use a solution of baking soda and water to remove the corrosion and dirt. A wire brush will help you to thoroughly clean the battery terminals. Wear eye protection for safety and take caution when removing battery cables.

Check and maintain your battery if possible

While most batteries today are the sealed “maintenance-free” type, some still have removable caps. These allow you to check the fluid levels. If you have this type, check it regularly in hot weather, as there may be some fluid evaporation happening inside. Top it up as needed with distilled water. Be sure to wear eye protection when doing this.

Replace your battery if necessary

If your battery is too far gone, you may simply need to replace it. Fortunately, this is a simple procedure that you or your mechanic can handle. It’s important to get a new one that has the same or better power rating, and to use a memory saver when you swap out the battery. For the longest possible battery life, your charging system should be checked, as well.

Get your car diagnosed by a professional

Symptoms of a bad battery

There are some telltale signs that your battery has a problem. Don’t ignore them — the situation will progressively get worse, eventually leaving you stranded. 

  • Your vehicle gets harder to start
  • The battery light on your dashboard comes on
  • Your headlights and interior lights get dimmer
  • Some of your car’s accessories won’t work
  • Your battery’s case is cracked, leaking or bulging

What your battery does

Your car’s battery provides the energy to turn your starter motor, crank the engine and get it started. It is also powers components like onboard computers, clocks, radios and alarms when the engine is off.

Inside the plastic case of most batteries, there are plates made of lead and lead dioxide. These are submerged in a liquid composed of two-thirds water and one-third sulphuric acid. This liquid allows a chemical reaction between itself and the plates, which generates the electricity your vehicle needs.  

Hot climates mean more batteries

As a rule of thumb, every 15-degree rise past the optimal 77-degree temperature cuts the lifespan of a car battery in half. Once the damage is done, it can’t be repaired. Those who live in southern Florida, the desert Southwest or anywhere else where triple-digit temperatures are considered normal are likely aware of what this means.

That new battery that would last five to seven years in a cool, temperate climate only lasts you two or three years. That’s the damaging effect of heat — it’s just a fact of life in these very hot areas.


Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.