In this paper I study the energetics of massive, charged black holes, pointing out the importance of the discharge process in increasing the energy loss of these objects. The decrement of the energy of a black hole is due to three contributions, namely the Hawking evaporation, the kinetic energy loss (for rotating black holes) and the pair production following the discharge process (for charged black holes). Here I evaluate the energy balance for Kerr, Kerr-Newman and Reissner-Nordstrom black holes, showing that, even if the discharge process is very fast, it can increase in a significant way the energy loss: that enables the emission of gamma ray bursts whose characteristics are similar to those of the experimentally observed bursts. Following this idea, one can explain in a quite satisfactory way both the peculiar bimodality observed in the gamma ray burst duration and their isotropic but inhomogeneous distribution.
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