Low Power Wireless (LPW) networks have recently been emerging as key candidates to offer affordable connectivity for the constrained devices in the Internet of Things (IoT). However, they also raise major security concerns due to the inherent security vulnerabilities of built-in communication protocols. By exploiting these flaws, an adversary can attack sensors or actuators in an LPW network and force them to execute energy-hungry tasks such as verifying unauthenticated garbage messages repeatedly. This attack, namely energy depletion attack (EDA), can drain the batteries of the devices rapidly and lead to soaring network-wide energy expenditure. Consequently, the offense can leave the victims disabled, and even shut down the whole network due to the battery exhaustion of all the devices. In this paper, we investigate existing studies and provide a systematic review of EDAs and defenses in LPW networks. Through this work, we conclude that most existing LPW technologies are vulnerable to EDAs. This paper also indicates the security challenges in LPW networks related to EDAs along with the potential research directions. While LPW technologies have already hit the market with the promising deployment schedules, our attempt can inspire the research community to enhance the security of underlying protocols that will shape the connectivity of billions of devices in the future IoT ecosystem.