Electrolyte Freezing

The freezing point of the battery electrolyte depends on the battery's specific gravity.
Freezing a battery can ruin the battery.
Protect the battery from freezing by keeping the battery fully charged.

With the green dot showing in the built-in hydrometer, the battery will not freeze until the temperature drops below -32°C (-25°F). A fully charged battery will not freeze until the temperature drops below -54°C (-65°F). Refer to Battery Hydrometer Displays Dark or Yellow Dot