This paper presents a single-inductor triple-source quad-mode (SITSQM) energy-harvesting interface in a 0.18-μm CMOS process. The proposed reversely polarized energy recycling (RPER) technique improves not only the conversion efficiency at low input voltage but also the system's output power range. The interface employs the buck-boost topology to convert energy from photovoltaic (PV) cells and a thermoelectric generator (TEG) to a regulated 1.2-V output. The proposed converter features four different operating modes, namely, harvesting, recycling, storing, and backup. The operating mode is automatically selected according to the input and load conditions using the automatic source selection mechanism. The experimental results demonstrate 25.3% efficiency improvement and 10 × output power range extension from the proposed RPER technique. The proposed SITSQM converter automatically manages three harvesting sources with 82.1% peak conversion efficiency.