A power consumption reduction method controls a rechargeable battery to enter a sleep mode after the electronic system is shutdown with the output current of the rechargeable battery falling under a first current value or the rechargeable battery is in a non-communication status for over a first delay time. When in the sleep mode, a control unit further controls the rechargeable battery to enter a power saving mode when the output voltage of the rechargeable battery falls under a predefined voltage or the RSOC of the rechargeable battery is lower than a percentage of FCC, and the output current of the rechargeable battery falls under a second current value or the rechargeable battery is in the non-communication status for over a second delay time. The method shuts down all power-consuming circuits and components under long-time idling of the battery, capable of preventing overly discharging and malfunction of the rechargeable battery.