Although this is the first battery I've used from them, K&F Concept is a well-respected brand for camera accessories in general, and these batteries have the clever twist that the Lithium Ion charge circuitry is built into the battery, so no charger is needed. Despite that, THESE BATTERIES HAVE A VERY COMPETITIVE PRICE -- less for these two than I paid for my first one with a built-in charger. There is a simple LED that lights red when charging and turns green when charged. The battery comes with a charging cable, but no USB power supply... which isn't a big deal; the cable is a little unusual in that the USB C end clips into the battery a bit more authoritatively rather than just smoothly sliding in.

It used to be that 3rd-party smart batteries often were recognized as "fakes" by cameras which would then refuse to operate with them, and some camera models and firmware revisions are pickier than others. Over the years, I've amassed quite a collection of NP-FW50 batteries and clones, including several rejected by my newer cameras or even by my original NEX-5 after I updated the firmware.

Incidentally, the main reason I'm still buying more NP-FW50 is that I have a fleet of Sony cameras (NEX-5, NEX-7, two A6000, A6500, A7, A7II, and two A7RII) that take this battery and about half of the batteries I have eventually (after multiple years of use) started to swell a little, which is a major danger sign for Lithium Ion batteries. If your batteries are becoming a tight fit into your camera, they are swelling too and you should properly dispose of them.

Anyway, I've tried using this battery in my Sony A7RII, which is one of the latest and presumably pickiest models taking this battery, and, happily, it seems to work identically to the Sony-branded original batteries. It's too early to say if this battery will hold charge as well as Sonys over time, but so far, so good. The battery fits the Sony cameras perfectly and has a distinctive two-color case, white on one side and gray on the other, which makes it easy to avoid confusing it with the ones that need a separate charger.

Overall, I think the concept of not needing an external charger is really good and worthy of a 5/5, although the benefit is reduced slightly by the fact that you still need to carry a USB cable to charge it. It does come with a charging cable, but it would be better if the battery itself had a pull-out USB head so you could just plug it directly into a USB power supply without the need for a cable. Unlike a very similar battery, there isn't much of a price premium for these over other non-Sony FW50 batteries that don't have a built-in charger. Thus, I very strongly recommend these...