You are correct, the computer uses an embedded Lithium battery. (very bad idea, Taiwanese are renown for their cheap design.) What will you do if your battery life wears out?.
In many other similar instances, draining the flea power after removing the battery worked.
You have tried all of the suggestions in my repertory including your own.
I am stumped ! The only thing I can think of is to consult a technician for a possible circuit issue.
Sorry Luciana, I can't help you further. If you do find a solution, please do let me know.
Best regards and good luck in TO.