I'm not familiar with the diamond mod so I can't say for sure but... I did watch a review on the knight rider (own one as well) and one of the points the guy doing the review pointed out was that when he tried using the batteries in his Provari it would not fire. The reason being that the lack of the nipple on the top of the battery made it too short to properly reach the contact.
For my own experience with the battery length VS the knight rider, besides the batteries that come with the unit An AW IMR fits fine but a protected Ultrafire BRC did not fit (could not screw end cap on all the way).
So if you have any probs with the diamond not firing with the knight rider batteries - Don't assume the mod is DOA Give an 18650 with a nipple a try first.
Hope this was helpful, and enjoy yer new mod!
