The two parameters that rule the low power consumption are: the operating voltage and the current consumption. Multiplying these two parameters we will obtain the total consumption of the device: we want this number to be as low as possible.
Very often it makes the mistake of associating the consumption of the device to the electricity consumption: the operating voltage directly reduces certain thresholds the current consumption and, consequently, the overall energy consumption, but the deduction “Low voltage = low currents” is not a rule.
We are constantly documented on the latest innovative technologies: small sized, with amazing computing power and low energy consumption, are typically powered at 1.8 V, 3.3 V and 5 V, even with a maximum current consumption of no more than 200 mA / h, while in sleep mode of 0.6 uA/h(!).
If you do the math, you can imagine a device that runs on battery power for a decade…