  The Tavis-Cummings (TC) model, which serves as a natural physical realization
of a quantum battery, comprises $N_b$ atoms as battery cells that collectively
interact with a shared photon field, functioning as the charger, initially
containing $n_0$ photons. In this study, we introduce the invariant subspace
method to effectively represent the quantum dynamics of the TC battery. Our
findings indicate that in the limiting case of $n_0\!\gg\! N_b$ or $N_b\!\gg\!
n_0$, a distinct SU(2) symmetry emerges in the dynamics, thereby ensuring the
realization of optimal energy storage. We also establish a negative
relationship between the battery-charger entanglement and the energy storage
capacity. As a result, we demonstrate that the asymptotically optimal energy
storage can be achieved in the scenario where $N_b\!=\!n_0\!\gg\! 1$. Our
approach not only enhances our comprehension of the algebraic structure
inherent in the TC model but also contributes to the broader theoretical
framework of quantum batteries. Furthermore, it provides crucial insights into
the relation between energy transfer and quantum correlations.
