TLDR: black eneloops give an actual 2400mAH (tested) to the radio, and will charge in the radio.
So to answer your question, I think they would be crap!
Either
a) they have a switchmode regulator in each battery → all you will hear is noise
b) they have a linear regulator → half the energy is lost.
c) whatever regulator, it might not deliver the 2+ amps the TX needs
d) A generic 14500 lithium (full length AA) is rated 800mAh. These are short 1/2 or 2/3 AA cells inside (at best) .
I am not believing the 1500mAh rating, even with a switchmode.
So maybe 1200mAh with a switchmode (but unusable for RX) or 500mAh with a linear regulator.
Or less
I tested my eneloop pro (black) at 2500mAh and some Aliexpress NIMH at 1850mAh
https://groups.io/g/ft817/message/112405
I am trying some NCR18650GA’s right now, rated at 3400mAh according to the test labels on them, but I am getting less than 2000mAh on the tester, not sure why.
So far I havn’t found lithium rechargeables with better tested capacity than black eneloops.