  A quantum battery is a temporary energy-storage system. We constructed the
quantum battery model of an N-spin chain with nearest-neighbor hopping
interaction and investigated the charging process of the quantum battery. We
obtained the maximum energy in the quantum battery charged by a coherent cavity
driving field or a thermal heat bath. We confirmed that for a finite-length
spin chain, thermal charging results in a nonzero ergotropy, contradicting a
previous result: that an incoherent heat source cannot charge a single-spin
quantum battery. The nearest-neighbor hopping interaction induces energy band
splitting, which enhances the energy storage and the ergotropy of the quantum
battery. We found a critical point in the energy and ergotropy resulting from
the ground-state quantum phase transition, after which the energy significantly
enhance. Finally, we also found that disorder increased the energy of the
quantum battery.
