  We theoretically investigate the enhancement of the charging power in a Dicke
quantum battery which consists of an array of $N$ two-level systems (TLS)
coupled to a single mode of cavity photons. In the limit of small $N$, we
analytically solve the time evolution for the full charging process. The
eigenvectors of the driving Hamiltonian are found to be pseudo-Hermite
polynomials and the evolution is thus interpreted as harmonic oscillator like
behaviour. We find that there exists a universal flip duration in this process,
regardless to the number of TLSs inside the cavity. Then we demonstrate that
the average charging power when using a collective protocol is $\sqrt{N}$ times
larger than the parallel charging protocol as for transferring the same amount
of energy. Unlike previous studies, we point out that such quantum advantage
does not originate from entanglement but dues to the coherent cooperative
interactions among the TLSs. Our results provide intuitive quantitative insight
into the dynamic charging process of a Dicke battery and can be observed under
realistic experimental conditions.
