  We consider a micromaser model of a quantum battery, where the battery is a
single mode of the electromagnetic field in a cavity, charged via repeated
interactions with a stream of qubits, all prepared in the same non-equilibrium
state, either incoherent or coherent, with the matter-field interaction modeled
by the Jaynes-Cummings model. We show that the coherent protocol is superior to
the incoherent one, in that an effective pure steady state is achieved for
generic values of the model parameters. Finally, we supplement the above
collision model with cavity losses, described by a Lindblad master equation. We
show that battery performances, in terms of stored energy, charging power, and
steady-state purity, are slightly degraded up to moderated dissipation rate.
Our results show that micromasers are robust and reliable quantum batteries,
thus making them a promising model for experimental implementations.
