I’ve uploaded the firmware, and this seems to have fixed the issue. I can insert the SD card, power it down, and successfully power it back on again. It works running off of the lithium battery alone as well. When using the Arduino IDE serial monitor, closing and immediately reopening the monitor after powering down doesn’t initiate communication - I have to close the monitor and open it back up again.
I don’t know if this is relevant, but it might be interesting - when I open the monitor and begin the communication, the first few characters seem to be completely random, which are followed by “Artemis OpenLog v2.4”. It might read something like:
⸮!)⸮KArtemis OpenLog v2.4
And all following lines appear normal. This happened with the previous firmware version as well, and the first few characters are different each time. In any case, I’m curious to hear what the culprit might be in all this. Thank you so much for your help!