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High-energy collisions can occur for radially moving charged test particlesin the extremal Reissner-Nordstr\"om spacetime if one of the particles isfine-tuned and the collision point is taken close to the horizon. This is ananalogy of the Banados-Silk-West (BSW) effect, first described for extremalKerr black holes. However, it differs significantly in terms of energyextraction: unlike for the original BSW process, no unconditional upper boundson mass and energy of an escaping test particle produced in the collision werefound for the charged version. We show that these results can be replicated forthe motion of charged test particles along the axis of a general extremalrotating electrovacuum black hole, also including the Schnittman-type processwith reflected fine-tuned particles. This brings the possibility of high-energyextraction closer to astrophysical black holes, which can be fast spinning andhave a small "Wald charge" due to interaction with external magnetic fields.Nevertheless, we find numerous caveats that can make the energy extractionunfeasible despite the lack of unconditional kinematic bounds.

Extraction of energy from an extremal rotating electrovacuum black hole: Particle collisions along the axis of symmetry