The best easy way to install Batocera (seems to be the only valid way), is to install onto an external USB drive or USB stick.
NO internal hard drive, NO internal partition, and NO dual boot "mambo jambo"!
(Etcher does NOT support internal HD.)
Install to the connected external USB drive.
-- Once the install is FINISHED:
If USB stick --> just plug, reboot and play!
If USB hard drive --> put the hard drive INSIDE the computer and Start computer..