Cold mornings drain car batteries. Get yours tested before the first freeze

Why cold weather is hard on batteries

A car battery makes power through a chemical reaction, and cold slows it down. AAA says that at 32°F a battery loses about 35% of its strength, and at 0°F about 60%. At the same time, the engine can need up to twice the usual current to start on a cold morning.

That is why a battery that seemed fine all summer can leave you with a click and no start on the first frosty day. AAA puts the average battery life at three to five years.

Signs your battery may not last the winter

• It is more than three years old.
• The engine cranks slowly when you start the car.
• Headlights look yellow or dim, or the dome light flickers.
• Warning lights come on, or the radio, heated seats or phone charger act up.
• The horn sounds weak.
• You smell sulfur (rotten eggs), or the battery case looks swollen, cracked or corroded.

Get it tested before it fails

A battery test takes a few minutes and tells you whether the battery can still hold a charge and deliver starting power. Many mobile mechanics test the battery, the alternator and the starter where the car is parked, and can replace a weak battery on the spot. Our price guide shows what mobile mechanics usually charge for a battery replacement.

If the car already will not start, our dead battery guide walks you through what to check first.

Cold weather costs you fuel too

The U.S. Department of Energy says a gas car gets roughly 15% fewer miles per gallon at 20°F than at 77°F in city driving, and up to 24% fewer on short trips of 3 to 4 miles. Hybrids can drop about 30% to 34%. Electric cars can lose about 41% of their range in mixed driving when the heater is on.

Electric cars and hybrids also have a small low-voltage battery that starts the car before the big battery is engaged, so it is worth testing too.

A five-minute winter checklist

1. Test the battery if it is three years old or more.
2. Clean any white or green crust off the battery terminals, or have a mechanic do it.
3. Check tire pressure often: cold air lowers it.
4. Use the winter oil grade in your owner’s manual.
5. Keep jumper cables or a charged jump starter in the car.