Sony doesn't have a battery grip for the APSC line of cameras. I guess that they don't think any of their APSC users are sophisticated enough to use a battery grip. However, the Meike MK-A6300 Pro, battery grip for the A6300, will also fit and function quite nicely on the A6400. It is not particularly expensive at $59.90 at Amazon.com https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
I suspect that there are less expensive battery grips sold on eBay which are actually the same grips as the Meike that have been re-branded...
There are things which I really like about this grip and some things that I do not like:
LIKE:
1. It gives me a better hand grip on the very small A6400 camera - especially when using a large lens like the 70-200mm f/4 G OSS...
2. The grip itself and the extra battery that it uses is relatively lightweight; far lighter than a Canon Battery Grip for my crop format 7D Mark-ii. I get the increased size at very little increase in weight...
3. The vertical shutter button is very handy when shooting portraits...
4. The two battery grip extends the battery life by somewhere near two times (I have not tested this) and will switch from the exhausted battery to the fresh battery seamlessly...
5. The grip fits the A6400 very well...
DISLIKE (I can work around these parameters)
1. I have to remove the battery grip to change memory cards...
2. In order for the vertical shutter button to function, an exterior corded connection between the camera and the grip is needed. It is very possible to jar this connection loose. However, if you are shooting video and don't need the vertical shutter button, the exterior connection is not needed...
3. The battery life left is only shown for the battery that is operating the camera. Total battery life for the two batteries is not shown...
4. I need to turn off the Battery Grip after using it or it will drain the batteries.
WOULD I BUY THIS GRIP AGAIN
Yes I would. This is the only game in town and if I want a grip, it has to be this one... I especially like it for shooting portraits in vertical composition and for using with a long lens. I tend to support the lens from beneath with my left hand when I am shooting with heavy glass. I don't just hold the camera. I also tend to take the tripod ring off the lens when I know that I will be using the camera/lens hand-held...
However, if you just need an extra half inch of so of depth for your shooting hand grip and don't need the extra juice of the dual batteries or the vertical shutter release button, an Arca Compatible L-bracket might do the trick if your tripod/monopod clamps are Arca Compatible. I use an eBay Fugasun (no kidding that's the name) bracket which only cost about twelve U.S. Dollars. It is very well made and it fits the A6400 exactly. In fact, I plan to leave this L-bracket on the camera all the time. The extra weight of the bracket is negligible.