  In this paper, we review the issue of defining energy for test particles on a
background stationary spacetime. We revisit the different notions of energy as
defined by different observers. As is well known, the existence of a time-like
isometry allows for the notion of total conserved energy to be well defined. We
use this well known quantity to show that a gravitational potential energy can
be consistently defined. As examples, we study the case of the exterior regions
of an asymptotically flat black hole and of the $\Lambda>0$ Schwarzschild de
Sitter case, where an asymptotic region is not available. We then consider the
situation in which the test particle is absorbed by the black hole, and analyze
the energetics in detail. In particular, we show that the notion of horizon
energy as defined by the isolated horizons formalism provides a satisfactory
notion of energy compatible with the particle's total conserved energy. With
these choices, there is a global conservation of energy. Finally, we comment on
a recent proposal to define energy of the black hole as seen by a nearby
observer at rest, for which this feature is lost.
