Battle Song Expertise is an bard feat, and was introduced in Dragon Magazine article Tools of Two Trades, for adventurers specializing in two weapon or implement groups.[Dr402] It is one of the feats associated with the White Lotus academy.
This expertise feat gives a +1 feat bonus to attack rolls made with any weapon with which you have proficiency, and with a wand or other item designed as a bard implement. The bonus increases to +2 at 11th level and +3 at 21st level.
It also provides a +1 feat bonus to the number of squares that the bard can pull, push or slide creatures with bard attacks and bard paragon path attacks.
Character optimization considers this feat to be a mandatory choice for bards specializing in the appropriate weapons (and using the slide bonus.)