Nikon EN-EL 15 and 15a fake check

One way is to weigh the original battery and the one you suspect is a fake. Not fool proof but a good way to start checking. Also the printing might vary somewhat or the logos are a bit different.

I just checked my new camera battery against my existing ones and they are all the same weight and same logo. Even the hologram has the 4 indentation marks on the edge.