Hi @TheGreenCastle,
This is a puzzle. I think you are the first customer with this issue - I don’t remember anyone else having the same issue.
It does sound like a microSD issue. It sounds as if the microSD is causing the power to “brown out” (drop to a level which causes the power-fail interrupt to put the Artemis into deep sleep). Please do try another microSD card. If you see the same issue again, then we will arrange a return or replacement for you.
The only other thing I can think of is that maybe the combined power draw of the Artemis + battery charge circuit (which draws 450mA) + microSD card (which can have a high in-rush current depending on the card) is causing your USB port to brown out. Please try your test again, without connecting the battery. That way the current draw will be much lower. Do you see a difference?
Very best wishes,
Paul