  We analyze a wireless communication system with finite block length and
finite battery energy, under quasi-static Nakagami-m fading. Wireless energy
transfer is carried out in the downlink while information transfer occurs in
the uplink. Transmission strategies for scenarios with/without energy
accumulation between transmission rounds are characterized in terms of error
probability and energy consumption. A power control protocol for the energy
accumulation scenario is proposed and results show the enormous impact on
improving the system performance, in terms of error probability and energy
consumption. The numerical results corroborate the existence and uniqueness of
an optimum target error probability, while showing that a relatively small
battery could be a limiting factor for some setups, specially when using the
energy accumulation strategy.
