Two or four Lith-ion batteries?

I am driving a 650nm laser at 378nm with a mohgasm linear driver.
(Mohgasm Linear Driver - $12.00 : Mohgasm!, Because it feels so good.)
I AM NOT heat sinking the driver as I do not plan to use the laser for extended intervals. My goal is to get the most burning ability and the brightest light for 10-15 second intervals. My only question is: should I use TWO or FOUR of these batteries? (Amazon.com: 2 X Ultrafire 18650 2400mah 3.7v Rechargeable Batteries: Electronics)

Thanks in advance!

Use two. Using more than that will create more heat.