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).