Laptop switching on and running the battery down from Hibernate

I'm still new to Windows 10 (home), from XP and recently bought a new HP laptop. I always leave the laptop with a full battery and hibernate overnight, with mains power turned off and the lid open. In the past week I noticed twice that the battery was about 80% in the morning so researched and made the changes to try and prevent wake states. Devices don't allow wake, task scheduler, deleting HP bloat, power saving options etc. Since then on Monday morning, the laptop battery was only 1% which I was furious about as I always avoid running a battery down as it causes damage. The battery is also 10.5 hours, and it was only left about that long or less, so it must have been on full power. There was nothing in the event viewer for the time it should have been off. I checked and amended the settings again and made a few more changes. (Including registry settingfor WindowsUpdate AU to 0. Last night I left it plugged in to the mains with a wattage meter. It did not switch on. Maximum watts used remained <1 watt. I have checked the battery and it is fine and works correctly in normal use.

So maybe I already fixed it but just checking if there is anything I might have missed. With an old netbook on XP, although it was never a problem, if I closed the lid or even temporarily turned off the power after hibernating, it would NEVER switch itself back on. It seems the HP with 10 does not do this, although I have not tried closing the lid??? If I have to shutdown rather than hibernate and/or close the lid, I'll have to but surely that shouldn't matter?

If it happens again, I'll know to use powercfg to see what waked it, although I expect it will be undetermined.

Of course, I have no idea why it did not shut down after doing its thing even until the battery was totally flat?

Any ideas? Obviously I'll leave it plugged into the mains until I can trust it. My fear is that it will be ok for a few days then do it again when I turn the mains power off and continue to kill the battery. (I gather 10 likes to reset settings during updates too) Surely it shouldn't be difficult to say switch off and remain off without having to remove the battery!!??

EDIT: One thing not tried yet is turning off "fast boot". I just found where that setting is, so turned it off. Don't know if relevent to this?

The two boot options of "fast boot" and "fast startup" are very different items.

The second is enabled by default in Win10, and I also have a new HP laptop that also runs down the battery when turned off -- and this was due to Fast Startup being enabled.

There are two ways to disable FastStartup in Win10; (1) through the Control Panel, and (2) through an elevated command prompt.

Control Panel - Open Control Panel --> Power Options.
Select "Choose what the power buttons do"
Select "Change settings that are currently unavailable"
At the bottom of the Window, under Shutdown settings, uncheck the box regarding fast startup

Elevated command prompt - run the following command:
REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Power" /V HiberbootEnabled /T REG_dWORD /D 0 /F

In both cases, reboot Windows.

NOW, FastStartup is disabled.

Already turned fast start off. Went into hibernate last night at 11:30pm. Windows turned my laptop on at 2:08am and left it on all night again. Obviously Microsoft don't care about the environment, destroying brand new batteries and turning computers on all night, any more than they do rushing out faulty updates making perfectly good equpment obsolute. Shame.

Boulder, you should also check, if your laptop is one of those called in for battery replacement program.

HP Notebook Computer and Mobile Workstation Battery Safety Recall

Sorry, if this has nothing to do with your case, but you didn't provide any laptop detailes and and part of of HP safety measure was:

Battery Safety Mode is only applicable to HP products affected by this recall. If the validation process identifies a battery as being eligible for replacement, the BIOS update should be applied and the system should be rebooted. During the reboot process, an option will be presented to enable Battery Safety Mode. Accepting Battery Safety Mode causes the battery to discharge and to cease future charging until Battery Safety Mode is disabled. HP strongly recommends accepting Battery Safety Mode so that the notebook or mobile workstation can be safely used by connecting to an HP power adaptor. For more information please refer to the FAQs tab on this website.