There were several models that used the Coinmaster 2 name going way back to the old BFO's. If we look at the three most recent Coinmaster II models they include the following:
Coinmaster 2/DB which was a rather simple models in a blue housing. There was one (1) 9V battery that snapped in a holder on the inside of the back housing door, and that only required a single 9-Volt battery clip.
The Coinmaster Classic II was in a more 'squarish-like' housing, black in color, and could be mounted in front of the hand-grip or removed (2 snap-lock buttons) and mounted under the fore-arm near the arm-cup. That Coinmaster Classic II used three (3) 9-Volt batteries.
If you have a most current Classic II SL, it is in the slim-line black housing and is mounted under the arm-rest upper rod and is not removable. There is a slide-in battery tray that holds 8-AA alkaline batteries. A physical description of the model, and color, and the full proper name would narrow it down. Look at the White's website under Owner's Manuals and find your specific model. If it is an older version and needs a battery pack, White's has it.
Monte