Some of the new reels claim to be braid ready and can be spooled with all braid but most of the older stuff will require mono backing or the line will spin on the spool while under a load. Penn uses a rubber base on its Battles to make them braid ready. I still use mono backing for filling the spool. You can go to some tackle shops that have bulk spools and fill with all braid if you want . You'll have to guess how much mono backing you'll need on your spool . Once you do that TIE your knot and fill the rest of the spool with braid.
