  Using the Newman-Janis method to construct the axion-dilaton coupled charged
rotating black holes, we show that the energy extraction from such black holes
via Penrose process takes place from the axion/Kalb-Ramond field energy
responsible for rendering the angular momentum to the black hole. Determining
the explicit form for the Kalb-Ramond field strength, which is argued to be
equivalent to spacetime torsion, we demonstrate that at the end of the energy
extraction process, the spacetime becomes torsion free with a spherically
symmetric non-rotating black hole remnant.
