In recent years, various service-oriented mobile robots have become more and more popular. These mobile robots need electrical power for continuous work for some duration using some kind of battery and hence a battery charging system is required. In order to increase the durability of robot operation, it is desirable to provide a power generation as well as a power supply system onboard the robot. This paper presents a design and implementation of a power supply system combining a fuel cell and lithium batteries to increase durability. It will be a new option to provide durable and environment-friendly energy for mobile robot. In this paper, we propose a charging logic to manage fuel-cell charging of multiple lithium polymer batteries, so that the power supply system can switch among lithium polymer batteries according to the load requirement. Experimental results of the developed power supply system on a laboratory mobile robot verified the effectiveness of the proposed design.