There is clearly a bug in the New 3DS XL Sleep mode. I have had it drain over night several times. This happens even if no game is loaded, e.g. you are on the home screen.
This was NEVER an issue with the old 3DS XL, nor is it with my older 3DS
I have not run tests, but it seems to be exascerbated by game cards in the slot - last night I had the 3DS Version of Animal Crossingd NL.
Has anybody else run into this?