A variety of data storage devices, methods and systems are implemented for control of memory associated with backup functionality. One such data storage device includes a power circuit that provides main power. The data storage device has a first solid-state memory circuit that maintains data in the absence of electrical power. A second memory circuit is subject to data loss in the absence of electrical power. A storage circuit stores energy and provides the stored energy to the second memory circuit in response to a loss of main power. A test circuit discharges a portion of the stored energy to provide output data indicative of power-providing capabilities of the storage circuit. A memory controller controls data transfers to the data storage device by temporarily storing data destined for the first solid-state memory circuit and setting the amount of memory available for temporary storage in response to the output data.