Molecular beam epitaxy-grown InxGa1-xN/GaN samples with indium fraction x ranging between 0.44 and 0.784 were studied by pulsed current-voltage (I-V) measurements at 1.7 K. The drift velocity, electron mobility, and electric-field-dependent power loss per electron were determined from analysis of the data. The drift velocity increased linearly while the electron mobility remained constant with increasing electric field. Power balance equations were used to obtain the power loss per electron as a function of the applied electric field in the range of 0 kV cm(-1) to 230 kV cm(-1). The results showed that the power loss per electron increased in the x range of 0.44 to 0.66, then slowly decreased in the x range of 0.66 to 0.784. The results obtained for the dependence of the power loss on the electron temperature are compared with current theoretical models for the power loss in two-dimensional (2D) semiconductors, which include both piezoelectric and deformation potential scattering. For all samples, the energy relaxation of electrons is dominated by acoustic phonon emission via piezoelectric interaction.