  We consider a quantum battery that is based on a two-level system coupled
with a cavity radiation by means of a two-photon interaction. Various figures
of merit, such as stored energy, average charging power, energy fluctuations,
and extractable work are investigated, considering, as possible initial
conditions for the cavity, a Fock state, a coherent state, and a squeezed
state. We show that the first state leads to better performances for the
battery. However, a coherent state with the same average number of photons,
even if it is affected by stronger fluctuations in the stored energy, results
in quite interesting performance, in particular since it allows for almost
completely extracting the stored energy as usable work at short enough times.
