I tested 5 under battery brands to replace the original battery for my a6400 (video available on YT).
This battery being 3-4 times cheaper than a Sony, offers a very light better battery life (sony 1h25 in 4K approximately, K&F Concept 1h32) and in addition offers you almost non-existent discharge against the Sony that loses a lot of storage (sony in storage a few months, remains 30% battery, K&F Concept 99%, and it is confirmed in time of recording in 4k, amazing..).
Until then, she beats flat with stitching the Sony...
... BUT (it needed one)...
... she has a small flaw that does not (as much) the Sony. The calculation of the% remaining on the K&F Concept is far from predicted, when the battery indicates 0% it actually remains more than 25min of recording, so you have to get used to keep recording but at 0% and evaluate about 20 min before changing the battery.
Apart from in certain specific cases, it is very uncomfortable but a shame...
(This is the same for the Sony at 0% there are still several minutes of recording.. 10 minutes of head but there is less to spoil if we change to 0%)

In the end excellent battery I use without problems for several months, I strongly advise this battery even faced with the shamefully expensive Sony and that does not hold the charge on time!

Even if I choose, I prefer to get used to calculating that I have 20 good minutes left at 0% (the K&F Concept), than to take out my device after a few months to realize that I have only 10% left (the Sony). (especially 4 times cheaper)

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