Properly assessing leg geometry and efficient thermoelectric (TE) materials are important for designing an improved and efficient TE system. Conventionally rectangular-shaped leg geometric features have been investigated for energy harvesting and cooling applications since the TE field's commencement. The engineering redesign of the thermoelectric leg's physical configuration opens a new research window to study the system's thermal efficiency and power output. Moreover, numerous studies have been conducted on improving the figure of merit over the last two decades by changing materials properties. A comprehensive survey on the non-traditional, i.e., non-rectangular-shaped leg configurations used in TE systems has been presented. Although no literature has been found on the experimental investigation with other geometries besides the rectangular-shaped TE leg, the trapezoidal-shaped leg geometry has received the most consideration in many analytical and numerical studies. Therefore, a trapezoidal-shaped leg has been proposed for the TE system, and prototypes are developed in this work. It is identified that the trapezoidal-shaped leg requires less material (nearly 25% less) and exhibits lower thermal conductance (around 27% less) in comparison with the rectangular-shaped TE leg. Furthermore, current numerical results show that the maximum COP of the trapezoidal-shaped prototype is approximately 32.5% higher than the rectangular prototype. This research also indicates that adding SiC nanoparticles with thermoelectric materials significantly improves the system's performance by decreasing the thermal conductivity (30.7 %) and increasing the Seebeck coefficient (7.5%). In addition, this thesis also focuses on the battery thermal management system (BTMS) with TE cooler (TEC) application. A synthesis of the literature is presented in a tabular format to indicate the existing BTMSs. Vibration from vehicles’ engines and bumpy roads affects the Li-ion battery's operation in terms of the operating temperature, lifetime, and driving time. Therefore, a series of experimental investigations have been conducted on the Li-ion battery's thermal management with porous media under vibration. The temperature drops around 26 ºC compared to the only battery itself under natural convection conditions. Moreover, a developed BTMS was investigated with phase change material using TEC, limiting the battery pack temperature within 37 ºC.