Cheaper Greenworks batteries will also fit a Kobalt...more or less. The battery is the same. The difference is the slots on the side that match up with the slots on the mower. There's a youtube video showing how to use a Dremel to easily mill a couple new slots on the battery to make it fit.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.