This research work investigates the power-current (P-I) and voltage-current (V-I) characteristics of the thermoelectric modules (TEMs) in series-parallel configurations under homogeneous and heterogeneous temperature difference (T) condition. To study its performance, 5 different series-parallel combinations were formed using 16 TEMs. The comparisons among the different configurations have been done to determine the optimal series-parallel configuration. The total load power extracted from 16 individually connected TEMs was 18.2W, which was placed as a reference load power. The optimal series-parallel combination for maximizing the load power is square series-parallel configuration, whose maximum load power is 95.5%, compared to the reference load power. Moreover, in square series-parallel configuration, the total internal resistance value that remains constant is equal to the internal resistance of a single TEM, and the total open-circuit voltage increases gradually on adding any number of TEMs. Thus, it produces higher load voltage and higher load current simultaneously, which is recommended to power DC micro-grid applications. Furthermore, the series, parallel, and square series-parallel configurations are connected as star to obtain 3 separate DC output to power the same application. The performance of TEMs under various configurations is analyzed, and the obtain results are verified experimentally.