Abstract Electrically powered robots are seeing increased adoption for field robotics applications. These applications typically require the platforms be deployed for extended periods, or traverse large distances. Power modelling therefore becomes important, as knowing the energy costs of operation is necessary for the estimation of maximum range and operating time, and the generation of energy-efficient plans. In this paper, we present a physics-based power model for the Swagbot platform--an omnidirectional electric field robot--which can be calibrated from a combination of GPS and proprioceptive data gathered throughout the course of normal operations. This model is then experimentally verified via endurance testing performed on cattle properties featuring uneven terrain. The model was demonstrated to predict the energy consumption for a pasture survey and a weed detection task to within 5% of the measured value.