Tethered quadcopters are used for extended flight operations where the necessary power to the system is provided through the tether from an external power source on the ground. In this work, we study the design factors such as the tether mass, electrical resistance, voltage conversion efficiency, etc. that influence the power requirements. We present analytical formulations to predict the power requirement for a given setup. Additionally, we show the existence of a critical hover height for a single-quadcopter tether system, beyond which it is physically (electrically) impossible for the quadcopter to hover due to the increasing mass of the tether load and any additional current increasing resistive losses instead of getting delivered to the quadcopter. We then present experimental resultsa for single quadcopter tethered system and a system with two quadcopters connected to the same power tether. Power supply readings from the experiments in various configurations are consistent with the predictions from the analysis (within 5%), which experimentally validates the presented analysis. A two-quadcopter system powered via a single tether is flown through a corridor to demonstrate one of the capabilities of having multiple quadcopters on the same tether.