Why Do Car Batteries Go Dead in the Winter?

car battery dead winter
It might seem like your car battery knows the exact wrong time to go bad, like in the middle of a winter snowstorm, but there is actually solid science behind battery failure. Jan Stromme / Stone / Getty

While it’s true that winter is a fairly common time for car batteries to die, some sources actually suggest that more batteries die in the summer than in the winter. So you may be dealing with a case of confirmation bias, but that doesn’t mean you’re totally off in left field. The science behind lead acid battery technology actually shows how both hot and cold weather can be unkind of the life and operation of a car battery.

Even though the hot weather is a real battery killer, for a number of reasons, cold weather is also hard on car batteries. This is why it’s a great idea to have your battery checked out before you head off on a summer road trip, while it’s an equally good idea to have some regular battery maintenance performed in the fall before it has the chance to leave you stranded in a snowstorm.

The Real Car Battery Killer: Temperature Extremes

Lead acid batteries are designed to work in a fairly large range of temperatures, but performance suffers in both cold and hot environments. According to Industrial Battery Products, lead acid battery capacity drops about 20 percent from normal in freezing weather, down to about 50 percent of normal when temperatures sink to about -22 degrees Fahrenheit.

In the same way that extreme cold reduces the capacity of a lead acid battery, high temperatures actually increase the capacity.

In fact, a lead acid battery can exhibit about a 12 percent increase in capacity at 122 degrees Fahrenheit versus 77 degrees Fahrenheit.

Of course, that increase in capacity doesn’t come without its own downside. Although higher temperatures result in increased capacity, they also result in decreased life.

The Reason Car Batteries Die in the Winter

There are three main contributing factors that lead to batteries dying in the winter: reduced capacity, increased draw from starter motors, and increased draw from accessories.

When you go to start your car, the starter motor requires a tremendous amount of amperage to get going. Under normal circumstances, your battery will offer no complaints, as the ability to deliver a lot of amperage over a short period of time is one of the things that ancient lead acid battery technology is terrific at.

However, a battery that is already getting long in the tooth can have a lot of trouble in the winter. And even if a battery’s capacity isn’t reduced by age, temperatures that are at or below freezing can even knock the capacity of a brand new battery so low that it can’t handle the demands of the starter motor.

When you look at a battery’s vital statistics, cold cranking amps (CCA) is the number that refers to how much amperage the battery can put out cold. If the number is large, that means it is equipped to handle higher demands than a battery with a lower number, which in turn means that it will perform better in cold weather, when capacity is diminished.

In some cases, especially in very cold weather, starters motor amperage demands can be even higher than normal, which can compound the problem. The issue is that motor oil gets thicker when the weather is cold, especially if you’re dealing with a single weight oil that doesn’t have different viscosity ratings for cold and hot weather. When the oil gets thick, the engine can be more difficult to turn over, which in turn can cause the starter motor to draw more amperage.

Winter driving typically also puts a higher strain on your battery, due to the demands of accessories like headlights and windshield wipers that tend to get used more often when the days are shorter and the weather is more likely to be inclement.

Unless you have a high-performance alternator, you may find your charging system struggles to keep up. And since the battery may already be suffering from reduced capacity due to cold temperatures, this can hasten the demise of an old battery.

The Reason Car Batteries Die in the Summer

In the same way that cold temperatures are hard on car batteries, hot temperatures can also have a negative effect. In fact, hot temperatures lead directly to shorter battery life. What that means is that a battery that is constantly operated at a balmy 77 degrees Fahrenheit will last about 50 percent longer than a battery that is constantly exposed to a temperature of about 92 degrees.

In fact, according to International Battery Products, battery life is cut in half for each increment of 15 degrees over a standard operating temperature of 77 degrees Fahrenheit.

According to the Car Care Council, the two main culprits behind dead batteries are heat and overcharging. When the electrolyte is heated up, it is more likely to evaporate. And if it isn’t topped up, the battery can be irrevocably damaged. Similarly, overcharging a battery can significantly shorten its life, damage it internally, and even cause it to explode.

Keeping a Car Battery Alive in the Winter and Summer

Anytime your car battery is operated outside the optimum temperature range, the fact is that there is a greater chance it will fail, whether it’s freezing cold or boiling hot outside. In the winter, one huge thing you can do in the winter is to keep your battery charged. According to Interstate Battery, a weak battery will start to freeze at 32 degrees Fahrenheit, while a fully charged battery won’t freeze until about -76 degrees Fahrenheit. Of course, it’s also a great idea to have your battery load tested, the electrolyte checked, and the connections checked for any signs of corrosion before the winter chill comes around.

In the same way, you can help your battery last longer in the summer with a little preventative maintenance. Since one of the biggest culprits of battery failure is heat, which causes electrolyte evaporation, it never hurts to keep an eye on your electrolyte throughout the warmer months. If the electrolyte starts to drop, then you can top it off before the problem becomes any more serious.