Can a Car Battery Freeze?

It's been so cold for so long this winter for much of the country that we'd be surprised if there was anything that couldn't freeze. But there was one question that came up recently we figured we could answer.

Can your car's battery freeze?

Yes, it can, says Gale Kimbrough, technical services manager for Interstate Batteries, though it takes truly extreme temperatures for a fully charged battery to freeze.

But if a battery is discharged because of damage to cells, poor connections or a charging system that isn't doing its job, the battery could start freezing at the same temperature as water.

"A 100 percent fully charged battery will not freeze until approximately minus 76 degrees Fahrenheit. A fully discharged battery can freeze at or around 32 degrees," Kimbrough said in a telephone interview. The difference between a fully charged and discharged 12-volt battery is not that big.

Related: How to Store Your Car for Winter

"When I'm talking about a fully discharged battery, I'm not talking about zero volts. A fully discharged battery is just below 12 volts. There's only about eight-tenths of a volt difference between a fully charged battery and a discharged battery," Kimbrough said.

A 12-volt battery has six cells, and Kimbrough said that if one cell is damaged, the voltage will drop below 12. Cells are connected in series, like Christmas lights, he added, and "you're never going to be any stronger than the weakest."

The electrolyte inside the battery is made up of about 25 percent sulfuric acid and 75 percent water. The acid interacts chemically with lead plates to create electricity, leaving mainly water in a discharged condition that is more susceptible to freezing. Water freezing inside a battery is "like ice cubes in a refrigerator," Kimbrough said. "When it freezes it expands, and when it expands it pushes those plates together and often causes a short between the positive and negative plates."

That damage will mean you need a new battery "in most cases, and if not immediately, then long term," he said.

The best way to determine the condition of a car battery is to have it checked by a mechanic or, for those comfortable with doing it themselves, using a voltmeter to measure the charge. Kimbrough suggests having the battery and charging system checked at the same time as other routine maintenance, such as oil changes.

Years ago, especially before sealed, maintenance-free batteries, most vehicle owners were more diligent about checking the battery and charging system because they feared their car wouldn't start in cold weather.

"The maintenance-free characteristics of batteries today often makes us forget how long it's been since it was replaced or looked at," Kimbrough said. "In the maintenance-free era, we don't think about whether our car is going to start or not. We're already down the road somewhere, in our minds."

Among warning signs that a battery no longer holds a charge are that the headlights become dimmer or a vehicle's clock starts to lose time, Kimbrough said. In some vehicles, the clock might reset to 12 or 1 o'clock. If a dashboard warning light for the charging system comes on, that usually means the alternator isn't recharging the battery.

Some batteries have indicators that typically glow green to show that a battery is fully charged, but Kimbrough said motorists shouldn't count on that because it's "just for one cell, so that doesn't have anything to do with the other five."

Cold temperatures make engines harder to start because the engine oil is thicker, requiring more effort from the electric starter motor. Cold weather also saps battery power. Interstate says a car battery loses 33 percent of its power when the temperature drops below freezing and more than 50 percent when it goes below zero, so just when you need more power, you have less to start your car.

"That's why preventive maintenance is a good idea," Kimbrough said.


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