Might be related to those sleep state stuff that microsoft keep pushing. I think LTT has a video about how it causes battery to drain while off. I think the solution was either shutting it down while unplugged, or while plugged in or something. If you always shut the laptop down with the charger plugged in try to unplug the charger before shutting it down and see if it makes a difference. Or the opposite. I don't remember which it was.

I would check the journalctl logs to ensure it is fully turning off. If here is still battery drain and you are sure the laptop is off, then its a hardware issue rather than software.

There's a feature to allow charging from USB ports while a computer is off, Lenovo calls it "Always on USB." That feature is constantly using power even when nothing is plugged in. To test if any ports have that feature power off the computer then try plugging in a simple 5v 500ma usb device to charge. If it starts charging then it has that feature and will drain power. If no options to disable in BIOS then as far as I know stuck :(

I've worked on a couple recent gen refurb laptops (dell and lenovo) with that feature but lacking any disable option in BIOS. I've tried to get into the habit of plugging in whenever not being used but still end up with things empty more often than I like. Very frustrating and I think only hope is future bios update to give that option.

My wife's HP laptop does this as well (she is running Windows). A previous laptop did this and a BIOS update fixed it. For most laptops the official response from manufacturers seems to be: eat shit.

Some level of self-discharge happens over time with even a disconnected battery, but that does seem greater than expected. I'd suspect hardware issues, to be honest. Batteries are fickle little creatures that deteriorate over time no matter what you do. Maybe it's misreporting the amount of charge left to the OS.

does this happen if you force it to shut down by holding the power button for +10sec, or if you remove and reinsert the battery after power off?

forcing a shutdown or removing and installing the battery, will ensure that the laptop is indeed shut down and not just halting during the shutdown process.

if you still have the same issue after this test I would guess your battery is dying, but if not you know that the issue is a software and not a hardware problem..

anyway, best of luck getting it sorted

This happened to my Surface pro 4 with both Windows and Linux. Could be a hardware issue.

How long does the battery last while powered on?

do you have any usb devices, like external hard drives, chargers or similar connected to it? a lot of the laptops allows for usb charging/supply of power even when switched off, and this could be one of the sources for the drainage.

try disconnecting all USB cables if any are connected and see if the problem disappears?

never mind, did not see the line about no connected usb cables until after posting

I have HP Notebook. This issue also happened to me. It was a battery issue. I just changed the battery.

Laptops now use the internal main battery as a replacement of the cmos rs2032 battery (in a lot of em at least).

Not that such a low draw cause this level of drain. Maybe the battery is going out as well.

Same with my Lenovo, not in few days tho but maybe in week or a two.

Maybe Intel AMT running? I'm not sure it can be disabled though.

I've had a similar issue with most of the laptops I have owned. The battery just discharges slowly when the device is turned off.

I have no idea what causes it or if it can be fixed.

Same for me with a MSI laptop, no solution

It may be exactly this, noticed by Linus Tech Tips: https://www.youtube.com/watch?v=OHKKcd3sx2c

If their solutions don't work, try this: https://www.youtube.com/watch?v=7JoFi5yXzZk