power supply

I built a 200mw laser pistol. I have a radio shack 2 aaa hobby box holding the batteries. I have room in the gun for one more cell, but the laser is rated at 4.2 v. If I added another cell it would raise the voltage to 4.5. What are the issues involved with over-volting this small of a diod?

Use rechargeable AAA cells. 3x 1.2= 3.6V. Still in the safe zone.

Hey thank you for the reply. I tell ya I went with the three higher grade lithium batteries. I just added a coolin fan and power switch into the mix. Now Im getting the full 4.2v max at the diode. Thats with full hot batteries of coarse.