  A battery is a work storage device, i.e. a device that stores energy in the
form of work for later use by other devices. In this work, we study the
realization of a quantum battery in a double quantum dot in series, charged by
two electrodes at different chemical potentials and optimized by a Markovian
quantum feedback protocol. Using the concept of ergotropy as a figure of merit,
we first establish a simple expression for the maximum ergotropy in a two-level
system, and then find the parameters under which a Markovian feedback can
achieve this optimal ergotropy. We also study the influence of interaction with
a phonon environment on the charging and discharging process of the battery.
