Under which condition is a lead acid storage battery most likely to freeze?

A lead acid storage battery is most likely to freeze when it is completely discharged. This occurs because the electrolyte within the battery, which is primarily sulfuric acid mixed with water, has a lower concentration of acid when the battery is discharged. As a result, the freezing point of the electrolyte rises, making it more susceptible to freezing temperatures.

When a lead acid battery is fully charged, the electrolyte has a higher concentration of sulfuric acid, which lowers the freezing point of the solution, making it less likely to freeze under cold conditions. Similarly, a moderately charged battery has an electrolyte concentration that is still sufficient to prevent freezing. Exposure to sunlight does not have a significant direct effect on the freezing point of the battery but can impact the battery's overall operating conditions. Thus, the condition of being completely discharged is critical in understanding the freezing risk for lead acid batteries.