Method and apparatus for assessing a time interval during which a refresh device can be maintained in a self-refresh mode by an associated energy source. The refresh device is initially operated in a self-refresh mode to maintain the device in a selected state. The time interval during which the refresh device can be subsequently maintained in the refresh mode is next determined in relation to an energy requirement value obtained during the self-refresh mode and an energy capacity value from the associated energy source. The energy capacity value is preferably obtained by fully discharging the associated energy source. Preferably, the refresh device is characterized as a dynamic random access memory (DRAM), and the associated energy source is characterized as a rechargeable backup battery. A selected test pattern is preferably written to the refresh device and maintained thereby during the self-refresh mode.