Will putting Lithium batteries in my laser damage it?

I bought a "50 mW" laser from http://www.amazon.com/gp/product/B000Y3N41U/ref=oss_product and I read in the reviews it is not a true 50mW. Someone said that if I put Lithium batteries in it instead of alkaline batteries, it will reach the true 50mW. But in the instructions, it says to only use alkaline batteries. Will putting lithium batteries in make it more powerful, and will it damage the laser?