Nick Odell wrote:

The 123 cells each weigh something between 13.8-14.0 grammes, the
little helicopter LiPo about 10.2g.

In the same way of measuring 18650 cells, a CR123A size is a 16340 cell.

I have a Fenix torch that takes a 26650 cell, it has a Fenix branded
cell 4800mAh (98g), according to my BT-C3100 charger, that capacity is
accurate.

Fenix sell various sized Li-ion cells, including a 16340 (19g), but only
with a capacity of 700mAh

https://www.torchdirect.co.uk/batteries-and-chargers.html

The mAh/g is better for the larger cells, obviously the metal casing is
dead weight, surface area to volume ratios and all that, which is one
advantage to LiPo with their flimsy "bags".

So I'd doubt any 16340 cell that claims 1500mAh capacity, if Fenix could
make one with double the capacity, why wouldn't they?

These 123s say Li-ion and 3.7v on the sleeve.

Did I squint and read on the photos that they have a minimum voltage of
2.75V? That seems quite low for Li-ion.