Herein, we present a fully integrated electronic product code (EPC) Gen-2 compatible battery-assisted passive (BAP) radio-frequency identification sensor tag integrated circuit (IC) with efficient power management. The key components of the tag IC include an adaptive radio-frequency (RF) energy harvester, a battery access controller (BAC), a storage capacitor charger, and a power-gated sensor block. External RF energy is efficiently harvested using dynamically controlled rectifying stages and a threshold-compensation technique. The BAC tightly controls the power path, cutting off leakage current from the battery. The power-gated sensor block supports multiplexed sensing operations in a power efficient manner. The sensor interface includes a chopper amplifier, a programmable gain amplifier, multiplexers, and an 8-bit ADC. For sensing data logging, custom designed nonvolatile memory is employed via one-time programmable memory. The digital control block is based on an EPCglobal Gen-2 standard that is modified to support the sensing operation. The tag chip was fabricated in a 1-poly 6-metal standard 0.18-mu m standard CMOS process. The tag IC consumes 1 mu A for leakage and active operation (0.1% duty), and the estimated lifespan of the BAP tag IC is about 0.2 year/mA.h.