  The Unruh vacuum is widely used as quantum state to describe black hole
evaporation since near the horizon it reproduces the physical state of a
quantum field, the so called in-vacuum, in the case the black hole is formed by
gravitational collapse. We examine the relation between these two quantum
states in the background spacetime of a Reissner-Nordstr\"om black hole (both
extremal and not) highlighting similarities and striking differences.
