@Colin_Adams
Note that the capacity of Ladda batteries
has changed during the years, i.e. they are
not created equal at all.
I made a swift test using Ladda AA/2450 mAh
and tried to ape your settings using an X-T4
and a Godox flash.
The first 6 shots came out OK, numbers 7 and 8
were totally black 
Have fun!
Claes in Lund, Sweden