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This paper demonstrates body-coupled (BC) data transmission and multi-source power delivery systems for neural interface applications. The implanted data transmitter and power receiver utilize an electrode interface rather than an antenna or coil interface for battery-free wireless transmission, enabling the external data receiver and power transmitter with patch electrodes to be placed away from the implant without requiring precise alignment, which is a critical issue in the conventional communication modalities of inductive coupling. Significantly, the implanted power receiver produces the supply voltage using ambient body-coupled 50/60 Hz signals from the Mains, on top of the 40.68 MHz wireless power source from the external power transmitter, to increase the recovered power level and the voltage conversion efficiency (VCE). The body-coupled wireless systems for implanted and external devices are implemented with integrated circuits (ICs) fabricated in a 180 nm CMOS process. When 650 mVpp AC voltage is applied to the implanted device, the power receiver recovers up to 780 μW with ambient (60 Hz signals) BC energy harvesting, achieving 93% VCE, while 600 μW is recovered without ambient (60 Hz signals) signal. The recovered power supplies the regulated voltage to the direct-digital signaling transceiver, which consumes 460 μW with an uplink data rate of 10 Mbps and a downlink data rate of 200 kbps, corresponding to an energy efficiency of 46 pJ/b.