An interpretation of the energy conservation law for a point charge moving in a uniform electric field

The standard interpretation of the energy conservation law accepted in the theory of electromagnetism maintains that a change in the field energy occurring in a volume is the sum of the energy increment in the volume due to the Poynting vector flow and the energy dissipated as heat in the interaction of charge carriers with the medium in which these carriers move. We show that the work done by an external electric field on a moving point charge is due to two sources: the energy arriving at the charge with the Poynting vector flow and a specific channel of energy supply to the charge originating from the interaction of the charge's field with the external field. Interestingly, at nonrelativistic charge velocities ($v\ll c$), 2/3 of the energy is supplied by the Poynting vector flow and 1/3 by the second channel. In the ultrarelativistic case ($v\lesssim c$), all of the energy comes with the Poynting vector flow.