Current, Jake.. Not voltage. 3.4 x 2 = 6.8V.. That means the current is not what it is set to - the voltage is too low for regulation... Charge the batteries fully, and measure the current by replacing the tailcap with your DMM in a current measuring range..
You also have to change the socket on the DMM for this usually, so that the current can flow from the batteries, THROUGH your DMM, and into the laser.