Within quantum thermodynamics, many tasks are modelled by processes that
require work sources represented by out-of-equilibrium quantum systems, often
dubbed quantum batteries, in which work can be deposited or from which work can
be extracted. Here we consider quantum batteries modelled as finite-dimensional
quantum systems initially in thermal equilibrium that are charged via cyclic
Hamiltonian processes. We present optimal or near-optimal protocols for N
identical two-level systems and individual d-level systems with equally
spaced energy gaps in terms of the charging precision and work fluctuations
during the charging process. We analyze the trade-off between these figures of
merit as well as the performance of local and global operations.Comment: 14+2 pages, 7 figure