Energy transfer through radio frequency (RF) waves enables battery-free operation for wireless sensor networks, while adversely impacting data communication. Thus, extending the lifetime for RF powered sensors comes at a cost of interference and reduced data throughput. This paper undertakes a systematic experimental study for both indoor and outdoor environments to quantify these tradeoffs. We demonstrate how separating the energy and data transfer frequencies gives rise to black (high loss), gray (moderate loss), and white (low loss) regions with respect to packet errors. We also measure the effect of the physical location of energy transmitters (ETs) and the impact of the spatial distribution of received interference power from the ETs, when these high power transmitters also charge the network. Our findings suggests leveraging the level of energy interference detected at the sensor node as a guiding metric to decide how best to separate the charging and communication functions in the frequency domain, as well as separating multiple ETs with slightly different center frequencies. © 2014 IEEE.