Welcome to the PSR Tutorial Forum, Elimelekh!
This is probably a translation error: By "Battery pack" you probably mean "Drum pack".
Unfortunately it is not possible with the description of the problem so far to give you specific advice.
Please state the exact name of the pack in question. Are you trying to load the pack directly into the keyboard (with a supplied .cpi or .ppi file), or have you previously successfully imported the pack (and possibly other packs) into the Expansion Manager (YEM) on the computer (.cpf or .ppf file) and then saved your own Pack Install file on the USB stick (which now doesn't work when installing on the keyboard?).
It is important that you select the file type .cpi or .ppi when saving the Pack Install file in the YEM, i.e. do NOT leave the default .cqi or .pqi (= Pack Quick Install) file type set.
Best regards,
Chris