Just a bit of history - the original EZ AA (XR-E Q5) did not support Li-ion, hence that original warning to not use >2V battery sources (both in the included manual and on 4sevens' site). This light was quickly shown to not perform to specs, and was recalled from the market.
The revised EZ AA (XR-E Q5) did indeed officially support Li-ion, as described in the accompanying manual (and confirmed to me by NiteCore directly). However, I believe 4sevens did not get around to updating the website. FYI, this is the light in my revised review.
The new XP-E R2 versions are unknown to me. But I would recommend you contact NiteCore directly, since I believe the warning on the 4sevens site continues to predate the newer versions.
:wave: