It was negative fifteen degrees in Chicago and my car would not start. Not a weak crank. Not a slow turnover. Just a sad little click and then silence. I was supposed to be at work in forty minutes.

Why Cold Kills Batteries

A car battery works through a chemical reaction between lead plates and sulfuric acid. Cold slows chemical reactions. At 32°F, a typical battery loses about 35% of its cranking power. At 0°F, it loses 60%. And if your battery is already old — three years or more — those numbers are even worse.

Meanwhile, cold engine oil thickens to the consistency of honey. So your starter motor is trying to turn a sluggish engine with a weakened battery. That is the double whammy.

Park Facing East

The morning sun hits the east side of your car first, warming the engine compartment slightly. Even a few degrees can make the difference between a start and a click.

Turn Everything Off Before Starting

Headlights, heater fan, radio, seat warmers — every electrical load draws from the battery. Turn off every accessory before you shut the car off the night before.

The Battery Blanket

For $25 to $40, you can buy an electric battery blanket that plugs into a wall outlet and keeps the battery warm overnight. If you park near an outdoor outlet, this is the single most effective thing you can do.

I replaced my battery the next day. It cost $120 and I never had a cold-start failure again.