Car batteries in winter: how falling temperatures affect them

The car battery is a fundamental element in any vehicle with an engine, even those that are neither hybrid nor electric. All vehicles need a place to store energy, at least to start up.

Without the electricity supplied, the combustion with which cars produce enough energy to move, whether on gasoline or diesel, is not possible. It all starts with the battery, and now that the weather is cold, this is one of the components that suffers the most.

How a car battery works

The cold affects all the components that make up a car. We have already talked about what happens to an engine when we start it in the cold in winter, but the battery is especially affected by low temperatures.

Batteries are those boxes that enclose the energy needed to get a car to start, move, have lights and even massage seats. Without that dose of energy that is later recovered through the alternator or with the use of kinetic energy, we would still be moving on horseback or by bicycle.

But this recovery is not infinite. A battery can store a limited amount of energy (Ampere-hours, Ah), at a given short current (Amps, A) at a given voltage (Volts, V). Although modern cars are quite electrically efficient, batteries have a finite life, which is usually particularly noticeable in winter, when temperatures drop.

Electricity comes from a chemical reaction. Although there are several types of batteries, the most common today are still lead-acid batteries: two plates (positive and negative) which are immersed in an electrolyte composed of water and sulfuric acid.

The batteries used in cars are composed of six cells, and each of these cells produces 2 Volts, for a total of 12 Volts. These cells are discharged every time we use them and they are recharged again by the chemical reaction itself or by drinking from the alternator, but as the chemical reaction progresses, a wear and tear known as sulfation process takes place.

When we start, we need a sufficient amount of voltage so that when we turn the key (or press the corresponding button) the starter motor moves the heat engine, turning the crankshaft. With a multimeter we can check the state of charge of the battery to find a figure that is always above 12V. From there down it is time to think about taking measures: either to plug the battery to a charger or to change the battery.

This happens because as sulfation progresses, the proportion of sulfuric acid in the electrolyte decreases, causing the voltage produced between the poles of the battery to drop. Consequently, the more times the battery has been charged and discharged, the longer it will age.

Battery life when it is very cold (or when it is very hot)

Extreme temperatures can cause the reaction inside the battery to be affected. For example, extreme heat can cause the water in the electrolyte to evaporate. However, the most acute signs of car battery depletion are shown in winter.

At temperatures close to or below 0°C the chemical reaction slows down, causing its performance to decline and resulting in an unusually sluggish starting phase. It can also happen that the motor does not move and we only perceive a repetitive clicking sound coming from the engine compartment.

Starting the car is when the most energy is needed. Starting a cold engine, having to move all the mechanical parts with oil in a more viscous state than normal, requires a high voltage to turn, something that is accentuated in periods of lower temperatures.

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