Lithium-Polymer (LiPo) batteries are becoming a popular choice for electric small low cost Unmanned Aerial Vehicles (UAVs). In case of a multirotor UAVs, a battery failure means a certain loss of the air frame. To fully utilize their potential and maintain mission safety, a monitoring system predicting battery behaviour is required. In this study a change in battery dynamics during discharge, and its effect of thrust produced by actuators is measured. Experiments simulating flight conditions are performed, and measured data are interpolated with double exponential and polynomial curves. An obvious similarity between the battery state-of-charge and produced thrust is observed. Due to conventional altitude controllers’ inability to cope well with changes in battery dynamics, a controller invariant to those changes is presented.