Why does cold weather kill your car battery?

Hook

Why and how does cold weather kill your car battery? The first freezing mornings of the year are when batteries quit. Here's what's happening under the hood.

Inside

A car battery makes electricity with a chemical reaction. Lead plates sit in an acid bath, and that reaction pushes out the current that powers your starter.

Cold

Cold slows that chemical reaction down. Around freezing, a battery can lose about a fifth of its capacity. In extreme cold, it can lose about half.

Demand

At the same time, the engine is harder to turn. Cold oil is thicker, so the starter motor needs even more power to crank it.

Squeeze

So you have less power available right when you need more. A weak or aging battery that was fine all summer just can't keep up.

Signs

Warning signs include slow cranking, headlights that dim when you start the car, and a battery that's several years old.

Tips

To help it out, get the battery tested before winter, keep the terminals clean, and park in a garage when you can. Lots of short trips also don't give it much time to recharge.

Close

So winter hits your battery twice, with weaker chemistry and a harder start. ThatsWhyHow.