The Zf, Z5, Z5II, Z6II, Z6III, Z7II, and Z8 use newer versions of the EN-EL15, currently the EN-EL15C. This new version has a higher capacity (2280mAh versus 1900mAh). This new battery can be used with the older Z6 and Z7 cameras (and other Nikon cameras that use the EN-EL15), but provides more capacity than the battery supplied with those cameras.
While some third-party EN-EL15C batteries are available, there is no guarantee that they’ll work with Nikon’s latest cameras. The Z8, in particular, seems to have stricter battery tolerances, and this is causing third party batteries to not be compatible. The Z6 III does not appear to work with current third party batteries as I update this page (see date below).
You can, however, use (some) earlier versions of the EN-EL15 with the Zf, Z5, Z6II, Z6III, Z7II, and Z8:
- EN-EL15 — powers the camera, cannot be charged via USB in the camera, doesn't support continuous USB power (may not work in Zf, Z6 III, or Z8)
- EN-EL15A — powers the camera, cannot be charged via USB in the camera, doesn't support continuous USB power
- EN-EL15B — powers the camera, can be charged via USB in the camera, does support continuous USB power on Zf, Z5, Z5II, Z6II, Z7II, or Z8 (but not on Z6/Z7)
- EN-EL15C — powers the camera, can be charged via USB in the camera, does support continuous USB power on Zf, Z5, Z5II, Z6II, Z6III, Z7II, or Z8 (but not on Z6/Z7)
A note about continuously powering the Zf, Z5, Z5II, Z6II, Z6III, Z7II, or Z8 with a EN-EL15C battery and the camera hooked up to USB: Nikon is using the PD (Power Delivery) standard. That means that any USB C charger that meets the standard can power the camera; you don't need Nikon's own charger. However, you do need to be aware that there are USB-C cables out there that don't support this standard. Be very careful to make sure you're using a PD-complaint charger and a PD-compliant cable.
There are also third-party batteries that work like Nikon EN-EL15 or EN-EL15A batteries, which the cameras can use.
Quite a few chargers exist for the EN-EL15 batteries (and will charge all versions of the battery). I like the dual battery chargers that have level displays.
Note that you wish to use USB charging (e.g. Zf, Z5II, Z6III, Z8, Z9) the USB Power Delivery source needs to be 27 watts minimum (9 volts at 3 amps).