I have several K&F Concept photographic accessories that, with a few isolated exceptions, stands out for offering very good quality products, at generally very low prices.
This is also the case with the set covered by this review, which consists of two batteries and the relative charger.

The two cells declare a capacity of 1100 mAh each, i.e. essentially in line with those of the Sony originals. Actually, in concrete use with both Sony Alpha 7R II and Alpha 6100, the autonomy is very similar to that offered by the standard batteries.
I did not find any sudden power drops, but the behavior during the download is progressive, as is the case with those branded Sony.
Note that the cameras mentioned also show the percentage of battery with these K&F Concept compatible ones, which are therefore recognized as if they were original parts.
The build quality is more than good, without detectable defects.
I would say that these K&F Concept batteries are equivalent to the best compatible batteries, which as far as I'm concerned are the Patona branded batteries, which I have been using for years.

The charger has two separate channels, which is why you can also charge one cell independently of the other.
Each channel delivers 730 mA of current, which means that a fully low battery will be recharged in approximately 1 hour and 30 minutes.
The fact that it is possible to power the charger itself even with a power bank and in general with any USB outlet that provides at least 2.1 A.
This particular model of charger it is more cumbersome than the other K&F Concept brand equivalents dedicated to the same type of batteries. This is due to the fact that the batteries should be inserted in it lying and not strung from above, resulting in an increase in the total volume.

With regard to the price, for 32.99 Euro it is already an excellent purchase.
In my case, I was lucky enough to buy it as 'used as new' for only 15 Euros, including Prime shipping (although the product was sold by a third party seller). I was given a product that has only the words used, because in substance it is indistinguishable from the new factory (perhaps it could be a reconditioned product, perhaps through the mere replacement of a faulty battery).
Given the excellent performance of the batteries and the useful two-channel charger, this is a very satisfying purchase.