Install:
-Put the dff and txd to gta3.img with an img editor Ex.: IMG tool 2.0
-Open default.ide. (sa folder\data\default.ide)
-Find "# melee weapons" and under that: "336, bat, bat, null, 1, 50, 0".
-Rename the 2 "bat"s to "batvc".
-You can start the game.

If you rename the files to bat, the icon won't appear ingame, because the icon texture has to have the same name as the files! (You can rename it, with txd workshop.) The files have different name, for those, who don't want to replace the sa bat, but want to add this as a new weapon.

Adding it as a new weapon:
-Watch Ryosuke's tutorial on Youtube.

csillam_faszlama