Other criteria that are important to specific applications include operating temperatures , pressures , energy efficiencies , high voltage stability , energy and power density (Wh L -1 , W L -1 ) , and charge time (time to full charge) . For example, charge times become very important in driving range considerations for electric vehicles, and voltage stability is important in applications where constant power outputs over long periods of time are required. Coulombic efficiency typically manifests itself in terms of time requirements and affordability due to extra costs associated with inefficiencies. Energy and power density typically come into play with applications where volume is limited, such as with consumer electronics and some medical devices. Operating temperature becomes important of course in any application that will endure extremes of either heat or cold while requiring a certain level of performance such as arctic research (low-temperature) or down-hole oilfield equipment (high-temperature) . Operating pressure similarly becomes important in extreme conditions such as deep-sea (high pressure) or space applications (low pressure) .