Older Batocera releases didn't support full 7Zip compression properly. But now, it's fixed. I finished to convert all my ZIP archives to 7Z last week. And it take awhile for very large fullset. I used LZMA2 with 2 threads and the "ultra mode" compression options to get the smallest 7Zip file size.
Everything perform properly with the Batocera 5.26 release I use. I compressed into 7Zip archive files all my roms and optical disc dump like CD/DVD too.
Like me, if you work with ClrMamePro to manage your roms, you should take a look here for 7Zip command line options you should used : https://www.emulab.it/forum/index.php?topic=4459.0