OK, so I am being a bit dramatic after all, but you have GOT to get this light!
Does it use a proprietary battery?
AFAIK any protected, button-top 21700 should work.
Is that because of the length or does it need to be protected?
It’s not quite a proprietary battery, but Fenix’s 21700 is extra-long and most 21700s and 18650s with the extender just don’t fit. So, effectively, it’s a Fenix-only deal.