  The development of fast and efficient quantum batteries is crucial for the
prospects of quantum technologies. We show that both requirements are
accomplished in the paradigmatic model of a harmonic oscillator strongly
coupled to a highly non-Markovian thermal reservoir. At short times, a
dynamical blockade of the reservoir prevents the leakage of energy towards its
degrees of freedom, promoting a significant accumulation of energy in the
battery with high efficiency. The possibility of implementing these conditions
in $LC$ quantum circuits opens up new avenues for solid-state quantum
batteries.
