This paper presents a small form factor dc-dc converter that can be used in a ladder architecture to provide state-of-charge equalization for large-scale lithium-ion arrays. A resonant switched-capacitor converter is implemented in a 180-nm bulk CMOS process that uses a merged-interleaving architecture to affect two-phase interleaving with only a single inductor. The approach has the advantage of reducing passive component volume for a given efficiency and voltage ripple constraint. A bidirectional current-mode control scheme is outlined that uses regulated zero-current switching and partial zero-voltage switching. The design also supports electrochemical diagnostic functions through a fully digital spectroscopic perturbation of cell current. Cell voltage and current are digitized through 10-b SAR analog to digital converters (ADCs), filtered and decimated for off-chip impedance extraction. The converter achieves 94.8% conversion efficiency in 1:1 balancing mode with a total board area less than 1 cm², and supports bidirectional power transfer >3.7 W.