  Work and quantum correlations are two fundamental resources in thermodynamics
and quantum information theory. In this work we study how to use correlations
among quantum systems to optimally store work. We analyse this question for
isolated quantum ensembles, where the work can be naturally divided into two
contributions: a local contribution from each system, and a global contribution
originating from correlations among systems. We focus on the latter and
consider quantum systems which are locally thermal, thus from which any
extractable work can only come from correlations. We compute the maximum
extractable work for general entangled states, separable states, and states
with fixed entropy. Our results show that while entanglement gives an advantage
for small quantum ensembles, this gain vanishes for a large number of systems.
