A bit of a YSK for noobs (like me).
I was setting up the RG35XX-SP with Knulli last night. They have an excellent little tool in the menus for checking for any missing bios files for the emulators. A few of the files I couldn't find anywhere, but I had similar (but not exactly) named files. For example, a DS emulation bios I was missing was dsi_bios7.bin but I had biosdsi7.bin.
Amazingly, the (I guess Batocera) developers include an 'MD5' hash of the required files in the message with each file name, so I was able to confirm these are actually the same files. eg for the file dsi_bios7.bin the MD5 was given as 559dae4ea78eb9d67702c56c1d791e81.
If you're not a software developer, you might not be familiar with hashes. They are basically a big number computed from every byte in a file such that if two files have the same hash, for practical purposes, the files are exactly the same.
To find the MD5 of a file in mac or Linux you just type md5 <filename> in the terminal (ed: md5sum <filename> on Linux - thanks @[email protected] ), or for little files like these, just drop them in an online MD5 calculator.
My bad - thanks for the correction!