The units are all coupled to a common quantized electromagnetic mode, and photons from the energy source mediate a long-range interaction between units, generating entanglement among them.

The enhancement increases as the number of units increases (specifically, when a quantum battery consists of N units, the quantum advantage scales as the square root of N).

They will be investigating the tradeoff between the quantum battery's charging power and its energy storage capacity.

Arxiv – High-power collective charging of a solid-state quantum battery, Oct 2017

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. Researchers present and solve a model of a QB that can be engineered in solid-state architectures.