A typical car battery can start to have significant trouble below 20°F (-7°C), and its starting power can be cut in half at 0°F (-18°C). While a fully charged battery's electrolyte won't freeze until around -70°F (-57°C), a discharged battery can freeze at just 32°F (0°C), causing permanent damage. The real-world limit isn't a single temperature but a combination of the battery's health, the engine oil's viscosity, and the severity of the cold.
The issue is chemistry. Cold temperatures dramatically slow down the chemical reaction inside the lead-acid battery that produces electrical current. This results in reduced Cold Cranking Amps (CCA), a rating that measures the battery's ability to start an engine in cold weather. At the same time, engine oil thickens, making the engine harder to turn over. A weak battery that might start a car in summer can fail completely on a cold morning.
The following table illustrates how temperature affects a battery's available power, assuming a battery with a 600 CCA rating:
| Temperature | Available Power (Approx. % of CCA) | Effect on Starting Ability |
|---|
| 80°F (27°C) | 100% | Optimal performance. |
| 32°F (0°C) | 65% | Noticeable strain, weaker batteries may fail. |
| 0°F (-18°C) | 40% | Significant power loss; starting becomes difficult. |
| -20°F (-29°C) | < 25% | Extreme risk of failure; permanent damage likely if discharged. |
To withstand deep cold, prevention is key. If possible, park in a garage. For extreme climates, invest in a battery with a higher CCA rating than your vehicle's minimum requirement. Using a battery blanket or a trickle charger/maintainer overnight can provide the necessary warmth and charge to ensure a reliable start. If your battery is more than three years old, have it tested before winter arrives.
