I want an 18650 battery with the following requirements:
I need it for 1x18650 lights like 502B, L2p, maybe a future C8, etc. So I guess length does not really matter, and I need button rather than flat top?
Has protection for over charge and over discharge, won't blow even if the protection fails.
Not sure about this (I don't completely understand how much current LEDs consume through direct drive): Cannot kill an XML when direct driven. 4A max? What happens if I DD an XRE or XPG or UV LED with such a battery?
Capacity is secondary, but the higher capacity the better.
Price is not a real consideration here, I'm willing to put about 25$ per battery delivered. But cheaper is better.
I'm a firm believer in the IMR (LiMN) chemistry. I'm donating/recycling all of regular protected 18650s. I'm getting my IMRs from lighthound.com and they are the AW brand.
I like the Xtar 2600, just be aware they are more like 18700 size and don't fit in every flashlight out there, but you mentioned you don't think that's an issue. Here's a few more to consider that have tested well here and all within your budget: