This type of battery is probably one of my favorite newer camera accessory tech that came out in the last few years. Now that a lot of cameras don't come with a separate battery charger, since they can change in-camera, these are a perfect way to charge a spare at the same time be it at home through a dedicated charger or computer, or on the go with a laptop or power bank. They of course still charge in a dedicated battery charger.

Now back to this specific K&F version. It charges at around 10W so its among the faster charging batteries of this type. The cheaper alternatives charge at 5W speeds, so takes significantly longer to top off. It is also the nicest looking battery in my opinion; the brown and the blue ones are more eye catching for better or for worse but these look great. Honestly I don't really care about the color too much but manufacturers like to flex it as a selling point so... And finally, although it doesn't quite last as long as the original batteries these do manage to last a more than adequate amount of time. Knowing it is from K&F you also do get the peace of mind of a quality battery, unlike some of the weird, random branded traditionally charging third party batteries that are super inexpensive.

Now for my one complaint with this battery, it would be the location of the charging port. Most of the other USB-C charging batteries for other camera brands have the charging port at one of the extremities, usually on the opposite end of the actual pins of the battery. This one is on the effectively bottom side of the battery. It still works but I feel it is slightly less convenient sometimes... this is purely a matter of preference though, and considering SmallRig's version also charges at the same location this might be a limitation to the internal structure of the EN-EL15C.

Overall, this is an excellent choice for USB-C rechargeable batteries for your Nikon.