"Sento la batteria."

Translation: I hear the drum.

[Were-cow]

First time with "batteria" it suggests drum kit ... I put drum kit
then it tells me the "kit" part is wroong

[f.formica]

Well, I think both you and duolingo are right on this one, in a way. Drum in Italian is "tamburo", while "batteria" is an array of objects, especially the given choice drum kit (a set of drums and cymbals), but it would be weird in English to say "I hear the drum kit"; you'd rather say "I hear the drums".