Thank you God, the battery WAS dead 🤣
Now we got our first problem. I did everything Phils did in that video, I also created two partitions on the new 240GB SSD in Windows 10 (for the alignment thing), a 4 GB one for Windows 98 and a 10 GB called Recovery, both FAT32, and set the 4 GB as active in FDISK.
I copied all Windows 98 setup files to the recovery partition E:, run the setup and Scandisk hang for like 5 minutes scanning E:, then it appeared a message that said something about a problem reading the last cluster and the drive needing the LBA. (I'm trying to use the Windows 98 italian ISO, so I don't know the exact phrase in english).
By the way, before I quit scandisk it says that C: had no error.
Edit: In the BIOS, IDE settings, there is an "Enhanced mode" for Windows 2000/XP and "Compatible Mode" for Windows 98/ME. I tried to set "Compatible Mode" but it doesn't work either.