Electrolyte Freezing

The freezing point of electrolyte depends on its specific gravity, or the state of charge. The higher the state of charge, the lower the freezing point. Since freezing may ruin a battery, it should be kept charged. A discharged battery can freeze at temperatures as high as -7°C (20°F). As long as the green dot is visible in the hydrometer, the freezing point of the battery will be somewhere below -32°C (-25°F). A fully charged battery will not freeze until the temperature falls below -65°C (-85°F).