Battery lifetime extension is a primary design objective for portable systems. Traditionally, mainly reducing average power consumption of system components has prolonged battery lifetime. A careful analysis of discharge characteristics and the adoption of accurate high-level battery models in system-level design open new opportunities for lifetime extension. In this paper, we introduce dynamic power management (DPM) policies specifically tailored to battery-powered systems. Battery-driven DPM strives to enhance lifetime by automatically adapting discharge rate and current profiles to battery state-of-charge. The distinctive feature of these policies is the control of system operation based on the observation of battery output voltage. The effectiveness of the proposed policies and, more in general, of the idea of accounting for battery behavior during system design, is proved by the experiments carried out on a realistic case study, namely, an MP3 audio player.