I have a PCB with a few radio modules on it. In its various states it currently uses anywhere between 100 µA and 100 mA. I can calculate how much time it spends in each of its states over a given year.
The radio modules on my PCB all have a wide acceptable input voltage range. My main processor and Bluetooth Low Energy module, for example, accepts anything from 1.8V to 3.6V. Right now I'm running it at 3.0V, using a step down DC-DC converter.
The battery is a 18650 lithium-ion (datasheet).
When fully charged, it provides about 4.3V. I'll step it down to 3.0V. The battery has a capacity of 3400 mAh.
Assuming the average current I'm drawing from it is 400 µA. My calculation for battery life is simply:
time (h) = capacity (Ah) / current (A)
3.4 Ah / 400 µA = about one year
Now, I know that in order to reduce my power consumption, I should run my circuit at the lowest possible voltage, so I'm considering changing my DC-DC converter and running my main processor and BLE module at 1.8V instead of 3.0V.
My question is: why isn't the voltage featured anywhere in my battery life calculation?