Power management is a critical component for wireless networks involving battery operated devices operating in harsh and unpredictable environments. This paper proposes the use of hybrid automatic repeat request (HARQ) for energy efficient power management that improves network reliability, guarantees quality of service (QoS), and extends network lifetime. A power optimization problem is first formulated under peak power, energy budget, causality (when energy harvesting is used), and QoS constraints. Relaxation of some of constraints is then proposed that is motivated by practical considerations as well as complexity issues. An efficient solution to the simplified optimization problem is then put forward to compute the optimal operating modes/parameters and an interpolation scheme is then proposed for real time implementation. Numerical results are then presented that demonstrate the effectiveness of the proposed design approach in achieving much lower energy consumption while guaranteeing the required communication QoS.