Battery life is determined in part by the number of cycles a battery is expected to provide over its operational lifetime. The more regularly and deeply a battery is discharged, the shorter this operational life will be. In addition, other factors—like lack of system maintenance, chronically undercharging batteries, or high battery temperatures—can shave years off a battery’s lifetime.
The original version of this battery guide included specifications for expected battery cycles at two different depths of discharge (DOD)—20 and 50 percent—but neglected to mention that the battery industry has no standard testing protocol for battery cycle-life specifications. The battery cycle-life data published by various manufacturers is determined with testing procedures set by each manufacturer, and some are more conservative with their cycle-life ratings than others. As a result, cycle-life data currently does not give an “apples to apples” comparison, and can misleading, which is why these specifications have been removed from this version of the article.
Standard testing protocols exist for newer technologies like inverters and photovoltaic modules. These standards are good for consumers and the renewable energy industry as a whole. Home Power strongly encourages the battery industry to develop standardized battery cycle life testing protocols. Doing so will help system designers and installers, as well as end users, in selecting the best battery for a given application and create realistic expectations for battery longevity.