Hi again Adam,
Thanks for taking the time to do some really solid measurements here to get a good idea of what the Artemis Nano will draw in different situations. We really do appreciate your work here along with your feedback about the quiescent current draw of the Artemis Development Boards.
The Nano was never designed with true low-power operation in mind, unfortunately, but, if you want to further try and reduce the current draw for your Artemis Nano, you are on the right track with disabling/removing the power LED and investigating what type of current the MCP73831 pulls without a battery attached. That should be a pretty low current draw but it's worth checking. One other note is to try powering with 3.3V directly to the 3.3V pins since that will bypass the AP2112K 3.3V regulator. You really should not see too much being drawn by that with 3.3V applied to Vin but it's another component that will add to the total current draw of the board. The other component to look at is the microphone. Disabling power to that will definitely help with power conservation.
As of right now, the best option we have for a dev board that has a Qwiic connector and is relatively low power is the SparkFun Edge
. We do have a new version of that with the full Artemis module onboard slated to release soon so keep an eye out for that but as far as I know, this will still have some issues for a true low-power solution since the mics and accelerometer are large current sinks (relatively speaking) and there is no easy way to disable them with this version.
Finally, I do want to again thank you for your feedback regarding the Artemis module and how we do not have a low-power option to truly showcase the abilities of the Artemis module. We have taken that along with other users' input into consideration and actively working on another board that will allow some user-configurable options to truly get a low-power development board using Artemis.