After a detailed analysis and discussion of two important characteristics of today’s battery cells (i.e., their current-capacity and current-voltage curves), this paper describes the design principles and architecture of a dual-battery power supply system for portable electronics. The key idea is to integrate two battery types with different energy capacity and current rate curves into the power supply system, and then use them in an interleaved manner in response to varying current requirement of the VLSI circuit that is powered by this dual-battery system. Analytical and empirical results demonstrate the effectiveness of the new battery architecture in maximizing the service life of a battery system with fixed volume (or weight).