  "A battery powers a device" can be read as "work stored in the battery is
being transported to the device." In quantum batteries, the total amount of
stored work can be measured by ergotropy, which is the maximal work extractable
by unitary operations. Transporting ergotropy is fundamentally different from
transporting energy, and here we find that ergotropy can be gained even when
the transmission channel is strictly energy conserving. We show that,
generically, ergotropy transport is lossy whenever the two systems start
uncorrelated. In contrast, for a large class of correlated initial states,
transport can be gainful. Furthermore, a single correlated state can be used
multiple times, allowing to transport without losses an order of magnitude more
work than the battery capacity. Correlations are thus a useful resource for
ergotropy transport, and we quantify how this resource is consumed during
gainful transport.
