  In many astrophysical scenarios the charge of the black hole is often
neglected due to unrealistically large values of the charge required for the
Reissner-Nordstr\"om spacetime metric. However, black holes may possess small
electric charge due to various selective accretion mechanisms. In this paper we
investigate the effect of a small hypothetical electric charge of a
Schwarzschild black hole on the ionization of a freely falling neutral particle
and subsequent escape of the ionized particle from the black hole. We show that
the energy of ionized particle can grow ultra-high and discuss distinguishing
signatures of particle acceleration by weakly charged black holes. We also
discuss a possible application of the proposed mechanism as an alternative
cosmic ray acceleration scenario. In particular we show that the Galactic
centre supermassive black hole is capable to act as a PeVatron of protons. The
presented mechanism can serve as a simple toy model of a non-rotating compact
object acting as a particle accelerator with a potential astrophysical
implementations related to the cosmic ray physics and beyond.
