## 1 Introduction  
In isolated rural locations, renewable energy sources, such as solar and biomass, are being increasingly used to meet electricity demands. Many off-grid areas cannot access grid-connected power supply, but these regions can take advantage of the readily available RE sources to power their homes and businesses. Due to the fluctuating nature of major renewable energy sources that vary depending on the time of day and season, an off-gridelectric grid that is based on renewable energy cannot guarantee an uninterrupted power supply [1]. Therefore, an efficient Energy Management Plan is essential for a reliable off-grid electricity supply, requiring the combination of one or two renewable energy sources with a battery storage system. The microgrid must be sized appropriately; if undersized, power losses will occur, and if oversized, the development costs may be excessive and lead to energy waste. To ensure the RE-based microgrid's benefits are fully realized, an efficient Energy Management Plan is vital [2]. This study conducted a techno-economic analysis of three different types of batteries, including LA, Li-Ion, and Ni-Fe, with a particular focus on the use of the LA battery technology in developing countries, such as India, Pakistan, Bangladesh, and Sri Lanka, due to its lower cost compared to other options. Although it has certain drawbacks in terms of its lifespan and durability, these batteries are still being used to provide electricity to remote rural areas in these countries. The life of these batteries is shorter than other types, and their longevity is dependent on the temperature they are in. This means that they need to be replaced every three to five years, which can present a challenge in more remote locations due to transportation difficulties. Thus, it is important to consider the technical and economic characteristics of these batteries, such as their lifespan, durability, round trip efficiency, high operating temperature capability, capital cost, replacement expense, and annual O&M cost, prior to initiating a project [3]. In order to tackle the issues discussed previously, this study proposes the use of Ni-Fe batteries. Although they may not be widely known, they are the most efficient and durable battery technology available today, making them suitable for off-grid solar and other green energy initiatives. Historically, Ni-Fe batteries have a 100-year track record. In the early 1900s, [PERSON] patented and developed them to be \"stronger than lead-acid batteries\". The first electric car was also equipped with this type of battery in the early 1910s. They were not used as starting batteries for cars but gained popularity in the 20 th century for forklifts, railroad applications, and standby power. In the 21 st century, these batteries are being utilized again, this time in renewable energy applications due to their durability, long lifespan, and incredible robustness. Unlike most other batteries, the life cycle of the Ni-Fe batteries is not impacted by their depth of discharge (DOD). This allows users to discharge them to 80% of their capacity without significantly reducing their battery life. By contrast, over-discharging an LA battery even once can result in a drastically reduced lifespan. The same cannot be said for Ni-Fe batteries, as their life expectancy is unaffected by discharging beyond 80%, and they can withstand overcharging without compromising longevity [3]. Optimization problems and theories encompass a wide variety of applied mathematics. Discovering the optimal size of a hybrid renewable energy system is a type of constrained optimization issue, which entail one or a few objectives in addition to integral or distinct variables as well as numerous linear or nonlinear limits. The renewable sizing issue is believed to have multiple local optimum solutions and a solitary global best optimal solution. Consequently, exploring the global optimal result is the most essential point to take into account [4].