I think there is a confusion here.
Firstly, the Nikkormat series was a "stripped" down version of the Nikon F and then F2.
The Nikkormat FT-2 was the second Nikkormat - following on the first model which was the Nikkormat FTN.
Unfortunately, Nikon was not too careful about nomeclature and at the same time that the first Nikkormat came out it introduced one of several "refinements" to the Nikon F. One of those "refinements" was the Nikon FTn (note the lower case "n"). This model included a built-in light meter powered by the merc battery.
I think that this is where the confusion is arising from.
I do know that the real Nikkormat FT-2 uses the simple 1.5 volt (e.g. LR-44) button battery as does, I believe, the Nikkormat FTN.
I also know that the Nikon FTn uses the now banned mercury PX625 (1.35 volt) for which you can buy the Wein replacment cells or seek one of the "homemade" replacements.
As to which camera you have, this is a simple deduction. Looking head-on at the mirror housing - is the name on the camera "Nikon" or "Nikkormat"?
If it is the latter then look at the top plate on the right by the film advance lever and see if it says: FT-2 or FTN
Then, just to be sure, look at the bottom plate and see if there is a small battery-sized screw-out plate (it has a slot in it and a US 25cent piece will fit there).
If it is a Nikkormat FT-2 or FTN - unscrew that cover and place in the battery. I believe it is +-side facing you (look at the bottom of the screw cover) or it is the other way!
If, however, when looking at the mirror housing of the viewfinder it says "Nikon" then you have a F-model. If it is a FTn with an electric meter then the battery housing is on the right side of the viewfinder housing next to the ASA knob etc.
Hope this helps.