My Olight i5T uses 2 AA batteries, and instructions say it’s compatible with NiMH and Li-ion batteries. However, instructions also say rechargeable 14500 Li batteries should not be used as LED damage may occur. This makes no sense to me, but being new to this technology, I’m obviously missing something. So why can’t rechargeable 14500 Li batteries be used in AA LED flashlights?
2 AA batteries in series gives you around 3v while 2 14500 batteries are around 8v, give or take depending on state of charge. Using them will in all likelihood result in a non-working flashlight.
Their instructions are a bit contradictory. I would not use the 14500 batteries.
One of the big difference between yours and mine is mine takes one battery and yours takes two. So that voltage is double like Sig said. I believe that would result in a much quicker destruction than my single cell AAA i3S- CU EOS.
I have an Olight i3S-CU EOS. I’ve had it for 5 or 6 years. I am pretty sure my instructions said do not use a Lithium-Ion 10440. Because of possible damage or destruction to the driver. I only use an Enloop battery. I’ve put a 10440 in there for very brief periods, 10 or 20 seconds at the most. It was almost twice as bright. But I don’t want to destroy the driver so I continue to use Enloops or an alkaline AAA in emergency.
Just to be clear, if you are using 2*AA batteries you are not using the Olight i5T but the Olight i5T Plus, right? 
SIGShooter replied and I don’t have anything to add! :+1:
Welcome to BLF 
Are you sure they say it’s compatible with Li-ion? Maybe they just said “lithium batteries” which is a completely different kind of technology. Lithium batteries are non-rechargeable and start at 1.6 V. Li-ion batteries on the other hand are rechargeable and start at 4.2 V.
Thanks for the responses. I get it, the voltage is additive (in series). Been a long time since I messed with electronics.
Correct, it is the i5T Plus. Thanks for the correction.
[quote=MascaratumB]
Yes, but actually the instructions say “Lithium-iron” [sic] battery compatible.
Lithium iron batteries do exist (LiFePo), but still have a higher voltage. Maybe they mean “lithium metal”, which is the lithium primary battery with 1.6 V I’ve mentioned previously.
Their “lithium-iron” almost threw me for a loop, too, first time I saw it in their manual. Better to say “lithium primaries” or disposable lithium-metal or something.
The Energizer Ultimate cells are lithium-iron-disulfide.
Basically the higher voltage of li-ion punches too hard for the components in the driver they are using (and/or the emitter itself, if all that voltage were to reach that far forward in the circuit). Like torquing a #8 screw to 20ft/lbs is ok but doing 40ft/lbs is going to make it go boom. The disposable lithium cells are just marginally higher voltage than alkalines and fully-charged NiMH so no worries.