I measured power consumption of various components of FORCE, and found that with everything on, FORCE consumes ~57mA of current:

When the solenoid is triggered this jumps to 200-300mA, but this is for very brief periods (~50ms).  So if we estimate and average of ~60mA of current, this means that the large 3 cell batteries (6600mAh) we've been using would provide about 100 hours of continuous operation.  Not bad!  The breakdown was:

• Adafruit M4 express feather - 29mA
• Force cell amps - 5mA each x 2
• MiniTFT screen - 18mA

Important to note, at the moment no power saving approaches are being used.  A simple approach that would save ~30% of the consumed power is to shut off the screen when the levers are not being pressed.  A more drastic measure would be to sleep the M4 processor and wake it up with a proximity sensor that detects when the mouse is near the device.  This approach would likely extend the battery life to >2 weeks.