In mobile applications, the energy consumed by operating system (OS) and application tasks primarily comes from a limited DC battery source, which imposes an upper bound to the amount of time available for execution of tasks. To achieve the best energy-aware quality of service (EQoS), it is important to prioritize the scheduling of critical tasks over non-critical tasks to improve overall performance while extending the battery life. Using the CSD (Combined Static/Dynamic) scheduler in the EMERALDS operating system as a basis, we developed EA-CSD (Energy-Adaptive CSD) with an energy-aware scheduling algorithm that executes tasks to achieve the effective use of limited energy by favoring low-energy and critical tasks. Our simulation of the EA-CSD shows that battery life can be extended up to about 100% with varying degrees of performance degradation of up to about 40%, and the actual values of both are fully customizable by the user through parametric adjustment.