Just curious.

I have tons of good NiMHs, but rechargable lithiums offer substantially more energy in the same size package. I have a lot of good AA/AAA gear and I'm not going to reinvest in a new platform anytime soon.

And yet, I have lithium ion rechargable spotlights that have been stellar in their performance. So I wonder if it's worth connecting the dots with my existing gear?

Yeah, got both a flashlight & headlamp, that came with rechargeable AA-sized (14500) 3.7v lithium ion batteries which have a USB port for direct charging. Find it handy for EDC lights.
But both will take NiMHs or lithium primaries, or even alkalines. Though output will be lower.

Spotlights I have little knowledge of, but would use larger lithium ion rechargeables for sure, like 18650 or even 21700 for the longer runtimes.

AA sized lithium tend te be too high of a voltage (straight up 3.7V) or stepped down, but still a little off.

Personally i'm phasing out AA/AAA sized batteries. They are only for things like bike lights, computers mouses, etc. Those run on mine supply of Eneloops NiMH's. The rest is getting replaced by Lithium based items. Either build in or accepting lithium cells.

That's interesting. The ones I see *claim* to be 1.5V. Are they known to run higher voltages than stated?

These will be used in headlamps and flashlights that were designed for alkalines not NiMHs. Maybe it's not worth the up-front battery cost to kludge lithiums in there?

There are lithium ion rechargeables that have extra electronics within them to reduce the voltage to a normal range for AA (1.2-1.5v)

Though not clear what advantage they'd have over regular rechargeable NiMh AAs.

The main advantage is 1/3 more capacity. But it's an expensive upgrade.

I still like the AA/AAA format for their flexibility when off grid or on the road.

I thought the advantage was their internal regulator outputs 1.5v rather than the 1.2v of a NiMH.

I haven't seen any AA sized yet with more capacity than an NiMH. Most seem to be in the same range.

Maybe I'm being to flashlight specific. But LEDs need atleast 3v to light up *. So using what is lithium ion based battery which outputs 3.7v only for internal battery circuitry to lower to 1.5v for only the flashlight to boost back up to over 3v doesn't seem efficient.

So prefer a flashlight that'll handle either a wide range, like 0.9v-4.2v or multiple ranges 0.9v-1.6v and 3.0v-4.2v.


* Also why 3xAAA is a common headlamp power source, in series they'll produce over 3v.

The problem is that Alkalines and NiMH aren't 1.5V either and have a different voltage dropoff, so i noticed devices not working properly (mostly battery indicators, but that is pretty important for things like avalanche beacons) and/or advised not to use them.

Alkaline is 1.5v nominal and NiCad and NiMH 1.2v nominal. Some devices won't work well with the lower 1.2v of Nicad/NiMH so these Lithium Ion with an internal regulator is supposed to keep the output at 1.5v so those devices designed for alkaline will work.

Devices that are essential to life have build in battery indicators and plenty of those will give an error when it noticed the voltage curve is incorrect (or they detect the differences and block it as it's not
intrinsically-safe in that configuration; ATEX/hazloc rated items). These range from avalanche beacons to industrial measuring devices. For smoke detectors; those tend to be more basic, but those will not provide battery alerts either when the voltage doesn't drop.

They will probably work with most regular items. But i personally don't have things that require more power density in AA/AAA form.

I appreciate the responses and information.

It seems the consensus answer to my question is "no." That's useful.

I'm going to start poking around for simple 18650 headlamps. I've been playing with the raw/unprotected ones for years, charging them directly off a 15W solar panel (monitored closely) and running old LED lights directly. They do seem to be better in many ways. We'll see if the protected ones are as good -- I have a charger on the way.

But all this belongs in another thread.