oomighoo try to use an disk partition manager like partition wizard or an linux distrib..... if you can view a "share" partition and others, delete all partitions exists and reformat the USB ! .... The windows can't "view" the batocera partition because it is an ext4 or other format partittion, but linux can do this best !
In windows you can try to use an program like "HDD Low Level format" to do an "delete" in table of partitions of you USB, so, you can reformat normaly !