Every source of information says to use lithium, not alkaline, not rechargeable.  I understand my no alkaline, that makes sense to me.  But not the rechargeables.
I don't doubt that the advice not to use rechargeable batteries is sound, I just don't understand the logic behind it.  Can anyone clue me in?

For what application?

I would assume because it's a night vision forum that he is referring to use in night vision. But that's just me, ;)

Wanna-be battery engineer here (which means a long time ago I worked for a
technical company and had a few long discussions with field engineers from
Everready and Duracell.)

I've tried digging on this question multiple times and never gotten a straight,
engineering/science-based answer. But you will find almost universally that
the NV suppliers say don't use them, as does the military.
(See page 45 of this issue of PS magazine, for example.)

The above source puts rechargeable AAs dead last in their list due to being unreliable,
but doesn't say why they're unreliable.

I speculate that's because the power profile of rechargable AAs dies super fast
at the end of the charge, but no one ever comes out and says this.

There's a tenuous engineering-based argument to not use rechargable AA's that
gets into the complexities of the high voltage DC-DC converter used in NV gear
to power the tubes. In a nutshell, when a normal battery gets used up, its voltage
goes down and internal resistance goes up, limiting the power it can put out.
This also happens with rechargables, but rechargables can supply significantly
more current at a lower voltage -- which a DC-DC converter will try to draw.
It's possible (but unlikely) that the higher current at a lower voltage exceeds some
component's max amperage specification. In reality you would have to go to
great efforts to actually design something to fail using rechargable v. normal
batteries and this seems counter to any good hardware design.

Yes, for use in night vision.  

And, if speaking to which application within night vision:  anything non-tactical.  Yard armadillo duty, checking out the stars, chilling in the woods.

Anything I can conceive myself actually doing. (Non-LEO,  no longer military, not an instagram influencer).

Don't rechargables (at least the NiMH modern ones) have a lower Fully Charged voltage? Something like 1.2v vs 1.5v?

I can see where some fancy electronics that need the full voltage of a AA would be upset to only see 1.2 on a fresh cell.

All of the above beat anything I can come up with. Cr123 rechargeables are 3.7.

In any case, I’m not curious enough to experiment with my new expensive toy.  I just wondered if it was an obvious, known, answer.

Ah!

I don't know about currently, but back in the past when I asked about it, this is what I was told.

Some rechargeables could be charged over what a standard battery would offer.  This higher charge could have various negative side effects like, "melting".

Military says no rechargeable because their capacity reduces as they age and they self-discharge slowly.  Thus your battery life changes and is very unpredictable.  Alkalines leak, don’t ever leave them installed long-term.  

The cost of energizer lithiums is trivial compared to the thousands of $ you spent on your toy.