I wouldn't worry about using a Fox plug with a 1.5 volt battery, or espically one of the little NiCad headlocks that are only 1.2.
I use Fox plugs with a power panel and they last a long time. I have an old panel with no rheostat but some sort of internal limiter that glows the plug without burning it down.
If yours has a dial, just hook up a plug and dial it up 'til the color looks good. Leave the EE stuff to professionals.