  In the present work we have studied collectives of active disks with an
energy depot, moving in the two-dimensional plane and interacting via excluded
volume. The energy depot accounts for the extraction of energy taking place at
the level of each particle in order to perform self-propulsion, included in an
underdampled Langevin dynamics. We show that this model undergoes a flocking
transition, exhibiting some of the key features of the Vicsek model, namely,
band formation and giant number fluctuations. Large density bands disappear as
the activity is further increased, eventually reaching a homogeneous polar
state. We unravel an effective alignment interaction at the level of
two-particle collisions that can be controlled by activity and gives rise to
flocking at large scales.
