In the systems that are fed by batteries, the duration of the energy supplied to the system is of great importance. To use high efficiency-motors in these systems can extend the battery usage time and it can be said that obtaining high efficiency-motors used in low power applications is rather difficult. In this regard, in this paper, design and optimization of a brushless permanent magnet DC motor have been carried out successfully, especially for a system fed by battery. By considering the high efficiency criteria, rotor design parameters such as rotor geometry, thickness and placements of the magnets, and embrace factor have been carefully examined. By obtaining the optimal rotor geometry providing maximum motor efficiency, some informative theoretical and finite element analyses are carried out. Electrical and electromagnetic distributions gained by the changes in rotor design parameters are presented in graphics. As a result of successive steps in the paper, the efficiency is increased; the cogging torque and magnet consumption are reduced for the motor under consideration, which is 20W, 24V, 3000 rpm with an inner-type rotor.