found a new host - unsure of batteries.

I am looking at using a kobalt flashlight as a new host and also use its stock power supply to drive a red 200mw diode. The flashlight accepts 2 x 3v cr123a lithium batteries. I am using a lm317 driver. Will these batteries drive the laser without any issues?

In practice, yes. Its a bit out of spec for the lm317, but most people are succesful in constructig a red laser that runs from 2 lithium cells.

That should work fine, the 6V should be enough for the lm3127+red diode.
Even better would be rechargeable Li-ion batteries of the same size, but 3.7V!

If I can run a 445nm diode off 2x18650s, then I suppose a red diode can be run too!

What do you mean a "bit out of spec"? I believe the cut off voltage for this circuit and diode is around 5.7 volts 4.5v for LD and 1.2v for the circuit. I know 4.5v is not enough as this only starts to light the LD. Is there a point where its too much voltage? Some of the more compact flashlights use 3 x AAA which can be replaced by 3 of the lithium batteries but that would push it close to 12v. Currently the setup is driven by 4 AAA alkalines which does work but the dry cells cant keep up with power demand.

Yeah, but make sure they're 3.7v rechargables, not 3.0v.

The LM317 linear driver starts acting funny at ~6v and below.