A fully charged lead-acid battery will not freeze until extremely low temperatures are reached because:

• A. The acid is in the plates, thereby increasing the specific gravity of the solution.
• B. Most of the acid is in the solution.
• C. Increased internal resistance generates sufficient heat to prevent freezing.
• D. The battery contains antifreeze additives.

Answer: (B)

Freezing point of the electrolyte depends on how much sulfuric acid is dissolved in water. In a fully charged lead-acid battery, most of the acid remains in the liquid electrolyte, so the solution is strongly acidic and its specific gravity is high. This higher acid concentration lowers the freezing point of the electrolyte, so it won’t freeze until temperatures are very low. If the battery is discharged, more acid is used up in forming lead sulfate on the plates, so the liquid becomes more dilute (lower specific gravity) and its freezing point rises, making freezing more likely. The other ideas aren’t correct here: there are no antifreeze additives in a standard lead-acid battery, and the heat from internal resistance isn’t enough to keep the electrolyte from freezing under typical cold conditions.