The Future of Energy is focused on the consolidation of new energy technologies. Among them, Fuel Cells (FCs) are on the Energy Agenda due to their potential to reduce the demand for fossil fuel and greenhouse gas emissions, their higher efficiency (as fuel cells do not use combustion, their efficiency is not linked to their maximum operating temperature) and simplicity and absence of moving parts. Additionally, low-power FCs have been identified as the target technology to replace conventional batteries in portable applications, which can have recreational, professional, and military purposes. More recently, low-power FCs have also been identified as an alternative to conventional batteries for medical devices and have been used in the medical field both in implantable devices and as micro-power sources. The most used power supply for implantable medical devices (IMD) is lithium batteries. However, despite its higher lifetime, this is far from enough to meet the patient’s needs since these batteries are replaced through surgeries. Based on the close synergetic connection between humans and microorganisms, microbial fuel cells (MFCs) were targeted as the replacement technology for batteries in IMD since they can convert the chemical energy from molecules presented in a living organism into electrical energy. Therefore, MFCs offer the following advantages over lithium batteries: they do not need to be replaced, avoiding subjecting IMD users to different surgeries and decreasing medical costs; they do not need external recharging as they operate as long as the fuel is supplied, by the body fluids; they are a more environmentally friendly technology, decreasing the carbon dioxide and other greenhouse gases emissions resulting from the utilization of fossil fuels and the dependency on fossil fuels and common batteries. However, they are complex systems involving electrochemical reactions, mass and charge transfer, and microorganisms, which affect their power outputs. Additionally, to achieve the desired levels of energy density needed for real applications, an MFC system must overcome some challenges, such as high costs and low power outputs and lifetime.