I (still) don’t have one of these lights, what does the spring end look like? Hypothetical: is there any opportunity to reduce the height of the spring to accomodate the longer cell?
I’d also go the path of least resistance, just don’t use the Vartas.
Completely not reccomended… I wonder if the button top is hollow or solid… Think there’s scope for removing 0.2mm of material? no, having looked at a teardown of AA, I think the button is likely hollow, so don’t do this.
Thanks guys to the both of you.
Of course, not using this kind of battery is the obvious by-pass option, but we at BLF like to find ingenious workarounds, don’t we? 
Moreover, I like the longer runtime of the Varta WRT the Eneloop.
Since the button is hollow, would squeezing it a very little bit in a vice allow to reduce the total length by 0.2mm without damaging the cell?
Another option: add a tiny solder blob on top of the contacts to make them protrude a bit further?
not sure that is logical.. im guessing the spring is already fully compressed when the Varta prevents closing…
making the contact taller is a good option
I would add actual metal, such as a piece of wire.. the solder alone will probably flow down the contact and not stay tall
A nice solution would be to find a metal o-ring, since even the narrowest available washers would be too wide.