Hi Greg,

Typically, the Lithium-ion battery sitting on the shelf will self-discharge about 3-5% in the first day or so and then 2-4% per month thereafter. Never let it get below about 20% of its capacity or else life time and total capacity will be degraded. The ullage rate is increased when the battery is stored in the camera. It seems I recall reading that the D500 battery discharged rather rapidly yield few shots than users expected. Nikon swapped batteries and such, but didn't explain the why. I expect that it was the battery's internal resistance was higher than specified and that affects both self-discharge rate and apparent capacity. I have seem this problem on Li-ion batteries we obtained from a vendor that were to be used in construction battery packs for communication radio systems. Our tests found these did not comply with our specifications and were rejected.

Thanks for the detailed explanation, Barry. Much appreciated. It’s good to know the “why.” Have a great day.
I have three battery packs for my D800 and rotate their use in the camera. On the first of the month, I check the one in the camera and swap it out if at two bars or less. It is then recharged. When in use, I always have one or both of the backup battery packs.

Bottom line is that I would keep a battery pack in the camera at all times.

Doc Barry