Nikon stuff costs a premium, until you compare them to performance.

ie cable release... I bought three off brand releases because I thought $65 Was a stupid expensive amount to spend on something like this... after those 3 failed quickly and suddenly, ( me without one and using it often) I bought the Nikon brand.. still have it after many years now. So it would have been much cheaper to have bought it in the first place.

The batteries are little computers in themselves. They provide the same amount of energy to the camera no matter their charge status. AS I am in the habit of turning off my camera between shots, I have never seen the need to buy a second battery. The only time it is an issue is when shooting tethered, or in assembly line product shots, where I am shooting multiple items on the same background camera mounted on a tripod etc. . I just watch it and recharge when I need a break anyways. I would use a power supply if I did it often enough.

Anyways, my battery is the same one I bought with my D800e when they first came out. I check the "remaining batter life" feature and will replace it when it becomes a concern. Until then- its been a fantastically worthwhile purchase ( It came with the camera), and have never needed a backup. even on my trips to Europe ( I'd recharge every night to top it off) or the back country away from electricity, where like I said I am in the habit of instantly flipping off the camera between shots.

This is my work flow though, and to be even faier- I have mostly prime lenses- so no power to the lens other than a readout, others may need a backup and once I forgot the battery in the charger all together- but that was my brainfart fault- not the batteries.