The average power draw of the RedEdge camera is approximately 3.5W (700mA @ 5.0V ), with peak currents of approximately 2A @ 5.0V. For calculating purposes, we recommend approximating the power draw of the camera as 4.0W to add some margin.
When considering what battery pack capacity to use, first convert from Amp-hours rating of the battery to Watt-hours by multiplying the Amp-hours rating of the battery by the average voltage of the battery. For example, a 3S 1000 mAh Lithium Ion battery pack would have a nominal voltage of 3.7V x 3 cells = 11.1V, yielding a Watt-hour rating of 11.1Wh (1Ah x 11.1V). This battery should power RedEdge for approx 2.7 hours (11.1Wh/4.0W). In reality, the actual endurance will be less than that due to losses in the battery and BEC.
For best results, the battery chosen should be able to supply currents of at least 2 Amps peak.