I don't think they should be merged, since there is a difference between fighting to seriously injury/kill (ie what the battle tag is for) and fighting due to an argument.
The naming though is confusing, so that probably should be resolved in some form. Changing the name for the trivial fighting for example would be one way, and another way would be having a tag like like fighting_seriously be aliased to battle, so that it appears and helps guide users away from the fighting tag and toward the battle tag.
