Electrolyte Freezing
The freezing point of electrolyte depends on the specific gravity of the electrolyte, or state of charge. Since freezing may ruin a battery, protect the battery.against freezing by keeping the battery charged. As long as the green dot shows in the built-in hydrometer, the battery will not freeze unless the temperature drops below -32 °C (-25 °F). A fully charged battery will not freeze unless the temperature drops below -54 °C (-65 °F).