Windows 10 issue.

You might try Windows 10 "startup repair".

It replaces some files that may have been corrupted during an update or other mishap.

Google "startup repair".

One sure way to test your battery is try and get another one that you can test your system with. That may be a pricey option and Ebay may sell you a battery in worse condition than yours. But it is an option worth considering.

You can also try and create another user account and see if Windows behaves better using that.

If so, transfer your files from the old user account to the new user account and when you are "absolutely sure" all of your files have been transferred, delete the old user account.

If this does not work do a complete windows reinstall.
Make sure you have all of your files backed up on several sources i.e. one drive and an external drive that is NOT connected to you PC when you do the OS reinstall.

Check the battery terminal connection and see if the plug in connection has been somehow damaged inspect it with a magnifying glass and light. It may only be partially getting contact.

Sounds like it is set to hibernate (suspend) when the battery gets low. Hibernation is when the laptop goes to sleep, it's different from a shutdown, in that when you wake it up you are back where you were. It sounds to me like your battery is failing, even if it is only 2 years old.