The small power pack for sphygmomanometers OMRON (Type HEM-ACW5-E) are too expensive compared to other suppliers. The decisive factor is the output voltage of 6V DC and 500mA. These power supplies are obtained cost-effectively. It is true that batteries can be saved. There are known rechargeable batteries that have a long life. In Omron sphygmomanometer 4 batteries size AA are needed. To protect your unit works even when no power outlet in close proximity!