The current goal is to minimize an embedded system consumption while maintaining all its features. Well-tuned power management becomes even more important in systems without any possibility of energy harvesting that rely solely on the battery power. The aim is a significant increase in the battery life without a desirable degradation in the quality of the service.A fuzzy rule-based classifier is intended to secure a simulation of the priority of the operation and the battery voltage. The energy consumption is a critical concern in the battery operated embedded devices. Power management is one of the most important consider aspects in low-power embedded systems design.This contribution studies the low power system in terms of the battery voltage level, depending on system priorities. The goal is to achieve the best possible efficiency of a whole device. The article offers a list of arrangements and applied methods having the most significant impact on the extension of the systems operating time.