Battery energy capacity in an application system is determined by the amount of electrical energy spent to the load and time consumption. The system reliability depends on the supply of electrical energy from the battery as the power source. The energy capacity of the battery will ensure the services provided by the unit device or equipment. As an example, the UPS system provides clean, conditioned, and continues power supply for sensitive loads such as airlines computers, data centers, communication systems, and medical support systems in hospitals, etc. Therefore, it is important to estimate the accuracy of the remaining battery capacity at any time. Generally, the UPS system provides a regulated sinusoidal output voltage with switching operation and will give power to the main applications. Some UPS inverters work by utilizing power from the battery modules. The switching operation that operated by the device, will generate high frequency ripple. Many other battery applications can be analogized as a fixed load. This means that the load does not change until the energy capacity of the battery is reduced. Both static and dynamic loads will affect the battery's internal resistance. Some literatures describe the important factor of the battery modules system performance and the degradation rate associated with battery internal resistance. This paper explores how the decreasing battery capacity using the DC current load correspond to the increasing battery internal resistance. We do some experiments on discharging battery with switching load current at 10 second measuring time. We investigate and analyze the difference effect of the battery capacity on the internal resistance battery. We conclude that on continues battery loading will decrease the battery capacity which corresponds to the increasing the internal resistance value.