Why is hot weather the death of car batteries?

You can be sure your car just won’t start when you’re hot and bothered and the temperature is soaring, or it’s cold and miserable and you just want to get to your destination. So, are batteries really more likely to let us down when the weather is least comfortable or is it just our imaginations?

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In fact, it’s true. Your car battery doesn’t like extreme temperatures for several reasons.

Hot weather

Batteries contain fluids that slowly evaporate and will do so faster in warmer conditions. Those low levels, in turn, damage the battery. Older style batteries could be topped up but modern ones are sealed to reduce the evaporation.

Hot weather also brings out the tourists and lengthens traffic queues. Batteries last longest when they are kept permanently fully charged but idling discharges them so you could be running with a low level of charge more of the time, reducing lifespan.

Cold weather

Cold engine oil is thicker so your battery has to crank harder to turn the engine, but battery power derives from chemical reactions that are slower in the cold. The shortfall makes a failed start more likely. Ironically, your battery holds the charge better in the cold but just doesn’t release it. Sometimes a battery that seems flat on a cold morning starts okay if you try it again at noon.

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In winter we also use heaters, wipers and lights more, increasing the likelihood of discharging the battery.

All weather

Despite their temperature sensitivities, the commonest reasons for a car battery to stop working have little to do with the weather.

We frequently damage them when we try to charge them as leaving them on too long can ruin them quickly. Topping up old style batteries with tap water is another fatal mistake. For advice see https://www.racshop.co.uk/advice/how-to-charge-a-car-battery.

A battery should last 5 – 7 years properly treated. When you replace them it’s vital to buy the right kind as they aren’t all alike. Consult a vendor or use their online battery finder tools such as http://www.grovesbatteries.co.uk/.

Driving habits can shorten battery life too. Short journeys with frequent on/off cycles cause more wear on many components but especially the starter and battery, and alternator faults can chronically overcharge them, wearing them out far too soon. The solution is to have your voltages regularly checked at a garage.