Car Batteries and Weather

Car batteries are powered by a mixture of water and acid, and this means that they are actually quite sensitive to temperature. Batteries can be damaged by extreme heat and by extremely cold weather too. Understanding the impact that different temperatures can have on your car’s battery will help you to prevent such damage, and to avoid situations where you get stranded with a car that won’t start.

Can cold weather affect car batteries?

Cold weather can have an impact on car batteries in a number of ways. It makes the engine have to work much harder to start, so more power output is required to get the car moving in the first place. It also reduces the power output that the battery is capable of producing. In addition, we tend to place greater demand on car batteries during the winter, since we run the lights more often, need to run the windscreen wipers more frequently, and usually run heaters as well. This means that the batteries drain more quickly simply because they are being used more.

Can cold weather drain car batteries?

Car batteries are constantly losing charge, even in mild weather, and even when they are not connected to anything. Cold weather does shorten the life of batteries, so they will hold less charge, put out less power, and as a result discharge more quickly.

If your usual usage habits involve many short journeys, then you will find that driving in the winter makes your car battery discharge very quickly. The best thing that you can do to avoid being stuck out in the cold with a car that won’t start is recharge your car battery every week during the winter months. Try to take your car out for a longer drive occasionally as well, because longer journeys do help to top up the battery a little.

Why do car batteries die in cold weather?

Car batteries are more likely to die in the winter for a number of reasons. The colder temperatures affect the chemical process that is going on inside the battery. This means that the battery is less able to hold charge, and that they produce less power. If the battery is already old or weak, then it will go flat very quickly.

In extremely cold temperatures, the battery will sulfate, and the mixture of acid and water will separate, causing the battery to freeze. Sometimes it is possible to revive the battery simply by allowing it to thaw out then recharging it slowly. Usually, however, a battery that has actually “frozen” is seriously damaged and should be replaced as soon as possible.

Can hot weather affect car batteries?

The idea that cold weather can affect car batteries is generally accepted, but did you know that hot weather can kill them too? What a lot of people don’t realise is that a lot of the problems that manifest themselves in the winter actually started in the summer. Heat can shorten battery life far more than cold.

Batteries contain liquid – a mixture of acid and water – and heat cases that liquid to slowly evaporate. If the fluid levels get too low, then the internal structure of the battery will become damaged. Too many people are accustomed to ‘zero maintenance’ batteries now, and if they have a battery that needs the cells to be topped up with liquid periodically, they may not realise it until it is too late.

Once a battery is damaged by high temperatures, you cannot restore the capacity that has been lost. Even batteries that are kept in storage will lose charge more quickly if they are exposed to very hot temperatures. A slightly cool, but not freezing cold, environment is the best choice.

Why do car batteries die in hot weather?

According to the BCI Failure Mode Study, car batteries are becoming increasingly resilient when it comes to heat. Modern car batteries – ones made using post-2010 designs, will see their battery life shortened by one year for every 12 degrees Celsius of extra heat that they are exposed to. Car battery designs have improved dramatically over the decades. A typical battery would last just 34 months in 1962, and by the year 2000 that had improved to 41 months. By 2010, car starter batteries are now up to an average life of 55 months.

Incidentally, there is a lot of anecdotal evidence to suggest that a car battery that is kept in the trunk of a car could last for a year longer than one that is kept in the engine compartment – in part because the engine compartment gets so hot.

Heat will cause the distilled water in the battery to evaporate, and this will deplete the liquid in the cells, which means that the metal plates in the cells are not protected, and the electrolyte balance in the cells becomes less than optimal. If one cell becomes damaged and produces less voltage, other cells will try to take up the slack. You can sometimes fix the cells by applying an equalizing charge that will boost the depleted cells – but again, over-charging healthy cells can damage them. With some batteries, it is possible to top up the liquid, extending the battery’s life. Zero-maintenance, sealed batteries, tend to last longer than open cell batteries.

Flooded lead acid batteries can be useful for hot climates, since they will last up to 20 years with good maintenance, but they need careful ventilation and are higher maintenance. In practice, few people get the full 20 year lifespan out of them.

You can prolong the life of your batteries by using them regularly. Do not leave a battery in a vehicle that is going to sit unused for a month or more. Recharge your batteries weekly during the coldest part of the winter, and try to park your car out of direct sunlight in a heat wave. If the battery allows it, top up the electrolyte levels regularly.

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