Abstract: Systems and methods to determine a power pack charging state. A difference between a first power pack capacity of a power pack at a first time and a second power pack capacity of the power pack at a second time is estimated, where the second time is a time duration after the first time. A determination is made that the charging state is “not charging” if the power pack capacity decreases between the two times. A determination is made that the charging state is “charging” if the power pack capacity increases between the two times. If a change in power pack capacity is not observed between the two times, the power pack charging state of the previous determination is used. Various techniques are used to determine the difference in power pack charging state.