A reader despatched me some further data on the completely different Nikon EN-EL15 battery variations based mostly on suggestions from Nikon help:
Q: Are you able to affirm if the battery life within the D850 is identical for each EN-EL15 black batteries and the EN-EL15a gray batteries? I’ve seen conflicting accounts within the press.
A: Battery life is identical.
Q: Is there a distinction in battery life with the D850 or the Z7 between these two batteries and the EN-EL15b (darkish gray) battery we count on to obtain with the Z7? I do know it contains compatibility with USB in-camera charging, however it’s battery life I’m taken with.
A: Whereas there are not any technical variations of the EN-EL15b battery (aside from USB charging), capability is equivalent to the EN-EL15a or EN-EL15 (20) when utilized in D500 or D850. EN-EL15b might be charged by way of USB – EN-EL15 (20) or EN-EL15a can not.
Further data is on the market right here.
Source from nikonrumors