Electrolyte Freezing

The electrolyte freezing point depends on its specific gravity. Since freezing can ruin a battery, it should be protected against freezing by keeping it in a charged condition.

When the green dot is visible in the hydrometer, the battery is a least 65% charged and will not freeze unless the temperature goes below -31°C (-25°F). The higher the state of charge the lower the freezing point. A fully charged battery will not freeze until the temperature goes below -65°C (-85°F).