Why Would Cold Temperatures Kill a Battery?

cold car battery with charger cables attached
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What You'll Need
Car battery
Block heater
What You'll Need
Car battery
Block heater

Of all the technology in your life, the battery under the hood of your car is likely to be the one to affect your day the most if it doesn't work. If it does, not many people give it a second thought—almost no one knows how their battery works, why it doesn’t work, what its limits are, or what kind of care should it be given.

Varying Car Batteries

There are many different kinds of batteries out there, each one of them designed for a specific purpose, some disposable and others rechargeable, some low voltage and amperage, others rating at much greater capacities. The most common battery inside a gas car is a rechargeable 12 volts (nominal) battery, rated at between 75 and 125 Ah (amp-hour), which is the maximum amount of power measured in Amps that battery can supply in one hour.

Now doing a simple calculation—if someone is washing and waxing his/her car in a nice summer day with the car stereo turned on and eating up a continuous 5 amps for a few hours, with a 100Ah battery, it will take 20 hours of playing that music to drain the battery to uselessness (100Ah / 5 Amps = 20hrs). But keep in mind that all those numbers (even the 12 volts) are only nominal for reference and not 100% accurate. Figure 1b shows a battery rated at 70 Ah:

car battery with technical information

Car Starters

However, the car battery isn’t just to power the radio. It's required to power up the starter while engaging a small gear onto the motor’s flywheel to turn the motor over, causing the pistons to slide in and create the explosions necessary to start the rotary momentum of the engine as an electrical surge reaches the spark plug.

A starter requires between 60 to 150 Amps to run idle without a load and 250 Amps to turn over an engine. So even a large 120 Amps battery doesn’t seem adequate to start a car, and that is why it is also tested for another very important rating called Cold Cranking Amps (CCA) which is the maximum amount of amps a battery can deliver for 30 seconds at 0° Fahrenheit (Figure 1a shows a battery at 590 CCA and 1b at 680 CCA), leaving the battery drained at an unusable voltage level.

Once the car gets running, however, the alternator kicks in powered up by the engine’s crankshaft and proceeds at rebuilding the battery’s charge. The CCA ratings of car batteries will be from about 350 up to over 600 CCA with of course their price tags following suite.

Battery Degradation

As rugged and mighty a battery might look, there are some conditions that can greatly deteriorate its performance and its lifespan, and two of those conditions are the battery’s exposure to extreme heat and/or extreme cold. Even for a well-maintained vehicle under normal use at mild temperatures, the battery’s lifespan will only be around an estimated five years, due to the constant charging/discharging cycles deteriorating the lead plates over time.

High temperatures tend to cause the battery’s electrolyte solution to evaporate, thus weakening its charge, and also causes the internal plates to corrode weakening its charging capability.

Low temperatures below -30° Fahrenheit can be harmful to a common car battery fully charged at 13.0 to 13.2 volts, but here again, these are nominal values only and can vary based on many affecting factors. There are also certain batteries manufacturers claim can withstand temperatures as cold as -50° F.

car battery charger

Safety Note: Never attempt to charge or jump start a battery if there is any chance it may be frozen, as this could cause it to explode.

Battery Chemicals

Gas car batteries are usually lead-acid batteries that produce a voltage by creating a chemical reaction between six cells made of lead-based alloy plates immersed in an electrolyte solution of 65% distilled water and 35% sulfuric acid. The chemical reaction between the plates produces approximately 2.1 volts per cell, adding up to 12.6 volts total when 100% fully charged. A battery that dropped to 12.4 volts is said to be at 50% charge, and at 12.0 volts is 25% charged. This is because a battery is considered fully discharged at 10.5%.

car battery charger pack

As a battery loses charge, the water separates from the electrolyte solution and when it gets low enough and is submitted to very low freezing temperatures, the distilled water is what freezes up inside the battery, even at warmer than 30° F temperatures.

Checking for Damage

It's very important to inspect a battery closely if you believe it to be frozen. During its removal, check for splits and cracks in the casing caused by the expansion of frozen water—these could let the acid leak out, causing possible injury.

According to some manufacturers, lead-acid battery power can drop almost 20% to 50% at temperatures below freezing. For this reason, and also because motor oil turns a lot thicker from the cold, it's much harder for the starter to turn the engine over, putting much more demand on the battery to start an engine in the winter.

As a precaution, many people get a block heater installed in the engine to keep the oil warm through the most bitter cold while the car is stopped. There are a few steps that can also be taken to further extend the life of the battery.

The car should be taken out regularly to give the alternator a chance to charge the battery. Just idling by the house is not enough because it doesn’t let the alternator turn fast enough to produce adequate 13.7-14.7 volts necessary for properly charging.

Keep the battery charged, especially if it’s getting older. A trickle charger can achieve this wonderfully.

If the car is to be left unused for a few months in the winter, the battery should be taken out and stored in the basement where there’s no risk of it freezing.

When storing the battery, it should never be sitting on the colder cement floor or surface—that would create a temperature sink which would eventually drain the battery.