Since yesterday I decided to do some tests. As I said before, format sysnand, do not link any account (This as Blythe93 said) seems to be the key, I deleted the emunand and recreated them, I have two SD cards.
Sysnand in 17.0.1, SD01 19.0.1, I'm testing with SD02, 20.1.0, 3-4 hours, has not happened the battery drain. Right now I'm going to perform the last test I have linked an account with linkalho, creating 2 users. I have only linked one of them. I also linked a remote with mission control. At 12:21 I have turned it off, about 3:00 pm, or 3:30, I will turn it on again, to see if it has drained something, according to some calculations in that time interval should drain about 15%.
It seems that recreating the emunand, and putting it all back on without a nintendo account linked, may be the solution, although I understand that it is very tedious to do. The aeroplane mode, which many commented on didn't work for me.
Once these 3 hours are over, I will edit the comment adding the result.
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Edit 1, 15:37. After 3h and 15 minutes, turned off at 100%, it is still at 100% after turning it on, I'll keep an eye out in case something changes, tomorrow, but for the moment in my case it seems to be solved.
Thank you very much
@Blythe93 for your help.