I have a relatively new (less than a month old) XPS15 9560 with the 97Whr battery.
I'm not sure how much the battery should lose charge overnight, but I've been losing around 10% in one night.
The whole system is completly powered off with no incoming from AC power at night, but still connected are the following items:
1 x USB connected to a Logitech unifying receiver for my wireless keyboard (which I switch off at night)
1 x HDMI to 1 LCD screen
1 x USB C dongle (Dell DA200) via HDMI to a 2nd LCD screen
1 x audio out to speakers
I did a test where I disconnected every connection. The laptop battery remained at near full capacity overnight.
So something is drawing power even though the system is completely powered down at night.
Has anyone else experienced something similar?