Killing someone in battle may or may not be heroic, depending on the situation.
For example: Being pinned down and returning fire and killing one of the enemy is survival/self defense.
For Example: Taking it upon yourself to rush the enemy while taking fire and killing the enemy is heroic for sure. He may have saved the lives of many of his fellow warriors.
Killing in the heat of passion can sometimes be charged as Aggrivated Manslaughter.
For Example: Trevor comes home from work and finds his wife taking it up the ass and the pussy, and sucking cock by three of the neighbors. Trevor freaks out, and pulls his legally concealed handgun out and kills his wife. Then without a blink of the eye he empties the remaining 13 bullets into his neighbors.
His defense? He didn't mind loaning his lawn mower to the neighbor friends, but his wife was off limits.