Battery drain or wrong reported battery charge on Precision/XPS?

I have a Precision 5540, the estimated battery capacity is 78,683 mWh, the battery is 2 years old.

I have modern stand-by disable am on Win 10. Overnight when the laptop is turned off I get significant apparent battery drain, 30-40%, the puzzling thing is that when turn on the laptop the displayed charge goes from say 40% to 1% then as soon as I plug in the charger the battery goes quickly back from 1% to its "real" level. See the screenshot below. The discharge rate when the laptop is on and operating is normal, as expected from a battery of this age. Do I have to reset the battery? So Windows is displaying the wrong charge level.