Gun you need a DMM to do a battery current draw test. Set the DMM to AMPs, don't go to low on your setting. Take the tail cap off and put one probe on the battery and one on the case threads. The DMM will act as a switch and give you a reading of what the laser in drawing. To give you an ides of what you may see.
I have a 405nm 2xAAA pen that draws 280ma, a 1x 18650 532nm that draws 400ma and my 3W 445nm 2x26650 draws 2.1 Amps.