No boost circuit, so only works with Li-ion or LFP, ’though not terribly brightly.
LFPs are pretty flat at ~3.2V from right out of the charger ’til they drop like a rock. Mine just blinked out 3.3V, so even freshly charged it’d be like running a Li-ion that’s just about to give it up.
Alkaleaks, though? No way.