  In a recent paper [1], the authors investigated the maximum stable throughput
region of a network composed of a rechargeable primary user and a secondary
user plugged to a reliable power supply. The authors studied the cases of an
infinite and a finite energy queue at the primary transmitter. However, the
results of the finite case are incorrect. We show that under the proposed
energy queue model (a decoupled ${\rm M/D/1}$ queueing system with Bernoulli
arrivals and the consumption of one energy packet per time slot), the energy
queue capacity does not affect the stability region of the network.
