Winterization

Temperature

As well as affecting self discharge rates, temperature affects battery performance in other ways. The optimum performance temperature range for batteries is 60 - 80 degrees Fahrenheit. At these temperatures, the battery will perform at 100% of its rated capacity. As temperatures drop, battery longevity increases, but performance drops. The battery goes into a state of partial "suspended animation" and only some of it’s potential power is available. You may have experienced this while starting your car in cold weather. (unless you are fortunate enough to live where there is no such thing as cold weather.) For example, at freezing (32 degrees Fahrenheit) some 65% of battery capacity can be utilized, but at zero only 40 percent is available.

Freezing

Freezing of batteries is a major concern of northern climate inhabitants. A fully charged battery typically will not freeze down to 70 to 90 degrees below zero, while a fully discharged battery is susceptible to freezing at +32 degrees. This is because of the chemical process which creates electricity in a battery. As a battery becomes discharged, the sulfuric acid in the electrolyte gradually bonds to the lead oxide in the battery plates. As this process continues, the electrolyte becomes less and less concentrated, until finally it is (theoretically but I wouldn’t drink it) pure water. Since water freezes at +32 F, the dead battery will then freeze at this temperature. Damage caused by freezing is mostly mechanical, I.E. the bursting of cases, plate breakage, separator failure, mechanical shorting, plate material delamination and many other woes too hideous to mention. Although batteries can sometimes survive even a severe freeze-up, there is always damage done, and reduced life can be expected.