I have the 2 1/4" Trutrak pictorial T&B. I had measured current consumption to be about 55 to 65 mA.
I installed a switch to select between the main electrical bus, or the alternate 9V battery supply. This allows the T&B to operate on emergency 9V power, and along with my other steam gauges, hopefully will allow me to get out of trouble when everything else electrical goes kerplunk.