  In recent years, energy harvesting has taken a considerable attention in
wireless communication research. Nonetheless, the stochastic nature of
renewable energy sources has become one of the research problems, and energy
storage has been proposed as a solution to deal with it. Initially, researchers
regarded a perfect battery model without energy losses during storage because
of its simplicity and compatibility in wireless communication analysis.
However, a battery model that reflects practical concerns should include energy
losses. In this paper, we consider an energy harvesting wireless communication
model with a battery that has energy losses during charging and discharging. We
consider energy underflows (i.e., the energy level falls below a certain
threshold in a battery) as the energy management concern, and characterize the
energy underflow probability and provide a simple exponential formulation by
employing the large deviation principle and queueing theory. Specifically, we
benefit from the similarity between the battery and data buffer models. We
further coin the available space decay rate at a battery as a parameter to
indicate the energy consumption performance. We further outline an approach to
set the energy demand policy to meet the energy management requirements that
rule the energy underflow probability as a constraint. We finally substantiate
our analytical findings with numerical demonstrations, and compare the
transmission performance levels of a transmission system with a battery that
has energy losses and a transmission system that consumes the energy as soon as
it is harvested.
