Thank you Les, Elsa, Akira and Øivind.
Les, one of my favorite photographic genres is astro-landscape photography.
During the time I had the D750 I shot a lot of long strings of 30-second exposures, often at high ISO's (3200-6400), and I could comfortably rely on getting over 200 images on a battery. I am actually pretty sure it would exceed 400 exposures on average.
Under the same conditions, my D500 does less than a hundred exposures.
Another favorite genre is air-show photography. This basically consists of relatively short exposures (usually between 1/80th and 1/250th), lots of burst shooting, full-time use of AF/C and FR on long prime lenses but infrequent image review.
Under these conditions, the D500 outperforms both the D750 and the D7000 I had before, easily getting more than 1500 exposures.
It is clear to me that my D500 uses it's power differently, and that this is not just a matter of shaving off a couple of percent at the bottom. I suspect the link Elsa posted may indicate that the D500 has a somewhat higher minimum voltage than earlier bodies.
I would like to understand if this is only my camera, and also I need to develop methods to get at least 150 and preferably over 250 exposures out of it without opening the battery door. Trying to make a star-trial with less than 100 30-second exposures is a waste of time, and time-lapse videos are even worse. For those, one needs at least 360 exposures (15 seconds viewing time at the lowest 24 frames per second).
What's more, I need to sort this out within the next 24 days, and the budget is pretty broken. A battery grip and EN-EL18 battery is out of the question right now.
