  Quantum information theorems state that it is possible to exploit collective
quantum resources to greatly enhance the charging power of quantum batteries
(QBs) made of many identical elementary units. We here present and solve a
model of a QB that can be engineered in solid-state architectures. It consists
of $N$ two-level systems coupled to a single photonic mode in a cavity. We
contrast this collective model ("Dicke QB"), whereby entanglement is genuinely
created by the common photonic mode, to the one in which each two-level system
is coupled to its own separate cavity mode ("Rabi QB"). By employing exact
diagonalization, we demonstrate the emergence of a quantum advantage in the
charging power of Dicke QBs, which scales like $\sqrt{N}$ for $N\gg 1$.
