Here are the top download links for Batocera ISO:
To get Batocera running, you'll need a way to "flash" the downloaded image onto your storage media:
Once you have downloaded the top file (usually a .gz or .xz compression), downloading it is only half the battle. You cannot just "copy" it to a USB. You must flash it.
Once you’ve grabbed your ISO file (usually in .img.gz format), you can't just copy-paste it onto a USB drive. You need to "flash" it.
That's not official (and illegal). But once you flash the official ISO, you can add your legally owned ROMs via the share/roms folder.