Improving efficiency for switched-inductor (SL) power-supplies is vital for battery-supplied microsystems such as wireless microsensors and portable devices. These microsystems idle mostly so efficiency in Discontinuous Conduction Mode (DCM) is crucial. Moreover, limited volumes of these tiny microsystems often lead to using tiny lossy inductors, which further reduce efficiency. Therefore, this paper theorizes how to select the optimal inductor, design the optimal power stage, and optimize the current profile to maximize efficiency in DCM, using insightful derivations. This proposed co-design of inductor and current profile is absent in the state-of-the-art. The theory is accurate, and the error is 0.3–4.9%.