Most battery applications spend more than 99% of their time in the sleep mode which makes their overall average power consumption very dependent on the power consumption while in sleep mode. Using the ATmega164P as an example, assume a 1.8V supply voltage operating at 1MHz in a 25ºC environment. The application is required to wake up for 10uS (micro second) every second to update the RTC (Real Time Clock). The average power consumption in active mode is 0.5mA (worst case) on the M164P, and 0.65uA in power save mode (RTC running). As shown by the calculation above, the application will be in sleep mode for 99.999% of the time. Also, the average power consumption (of 0.655uA) calculation shown above is based on the percentage of time the device spends in active and sleep modes. As a comparison, a typical AAA battery has a rating of 1200mAH and at least two are needed to get above 1.8V. Self discharge of such a battery is a minimum of 3% per year at 25C, worse at higher temperatures. Therefore, self discharge will be at least 72mAH. There are 8760 hours in a year, so an average current consumption of 8uA also consumes 72mAH/year. Current consumption of the AVR in this case is insignificant compared to the self-discharge rate of the battery.