How Many Batteries Will I Need For My Con? (calculation question)

I plan to use a Crystal Focus and a tri-cree with premium speaker but I don't know how many total watts they draw. I plan to use a 3400mah replaceable battery. I want to have my saber on for as long as possible across an 8 hour con and will want to be able to recharge them in the night. I plan to have two sabers with the same setup (one blue and one red tri-cree).

Is it safe to say I need 3 batteries for each saber to get at least a 4 hour total run time for each saber?

Correct.

Thank you. Also as far as the blade holding screw, does tcss provide them too? Am planning on placing my order once I get this info.

Yes, look in the screw section.