Bullet plug, often called a trailer plug.
You won't find it in a car place though, because that is battery wire size,, like 12 gage.
Replace that shitty plug with a set of Anderson power poles, or better 4mm hobby bullets from a RC toy store.
Mark your wires very carefully before you cut anything,, I have seen that type of plug used, so that positive is red on one side, but black is positive on the other.