While the Sony A7 series of cameras brings many great features to the table there are two "flaws" to the camera for many people. The first one is almost universally mentioned; the small batteries don't come close to matching the stamina of the much larger batteries in cameras like DSLR Nikons, Canons and the mirror-free battery champ = the Panasonic GH4. The second, more egregious failing of the series is the tendency for them to overheat; especially when shooting 4K video.
In the first instance there is a cheap and relatively efficient workaround; just buy some extra, third party batteries like the Wasabi Power models. Keep a couple extra in your saddlebag and you're good to go for the day. Unless you are shooting video and then you might want to consider increasing the size of that saddlebag... But, if you stock up on batteries you won't be caught short with a non-working camera.
The second fault is much more vexing for a working photographer, or for any photographer that expects reliable camera operation, and that's the tendency for the cameras to overheat. Once that overheat indicator becomes visible
on your status screen you can pretty much count on the camera shutting down a short time later. It's can be a very frustrating occurrence for any photographer or videographer but if you are using these cameras to create content for paying customers it might just be a job killer. The precursor of poverty. The camera that had so much promise...
A firmware upgrade for the A7xii series cameras allows the cameras to run a bit hotter before entering the ultimate frustration zone but it did not ameliorate the problem altogether. I shy away from using my A7Rii for video outside (we live in Texas after all) and generally substitute the stalwart RX10ii or RX10iii instead. I've run each of those cameras for as long as a battery will last while shooting video and have never had any issues with heat. But owning a $3200 camera that you can only shoot video with in locations with ample central air conditioning is a bit....counterintuitive.
I've read that pulling the LCD screen away from the body can help, and, I've had friends rubber band an ice pack to the backs of their cameras in a Rube Goldberg attempt to prolong the pre-heat run time but neither of those solutions seems foolproof.
I recently read some interesting stuff on one of the fora on DP Review (Sony FF e-series) which suggested that using a battery grip would reduce or eliminate the heat issue. The thinking is that a large percentage of the heat generated while shooting these cameras (which have no venting to the outside air) is from the batteries. Easy to verify this, just shoot ten minutes of video and then dump the camera battery out into your hand. I guarantee it will be warm to the touch---in some cases, hot. Since the battery is inside the sealed camera enclosure there is no where for the heat to go. It spreads through the interior of the body, meeting up with the heat generated by the sensor and the processing chips and the combination quickly boost the internal temperature of the small space.
If you add a battery grip to the mix the only thing in the camera's battery compartment is the connector part. The battery and the heat it generates is separated from the interior of the camera and any heat generated by the battery is kept outside the working eco-system of the camera.
I tried this out yesterday with a third party battery grip from Vello. I stuck a couple batteries in the grip and bolted it onto the A7Rii. I set the camera up outside the studio but not in the direct sun. It was 96 degrees when I ran my test. The humidity was quite high and generated a heat index of about 106 degrees farenheit. I set the camera to shoot 4K video, with the rear screen active and then let it run. Which it it did for the full 29 minute limit with no heat indicator appearing.
While I had upgraded the firmware to 3.0 which is supposed to deal with the issue I still experienced a few heat warnings when working in hot spaces with the camera in 4K. To be able to run right up to 29 minutes without triggering a warning is comfortable.
So, you could by the Sony grip for +$300 or spend $79 on the Vello grip. I bought one a while back for the A7ii and it has not failed in almost 9 months of use. I bought a second one just to use on the A7Rii and expect it to arrive tomorrow. A small investment to gain extra battery life AND a cooler running camera.
The interesting idea to me is that this solution should work with just about any current camera. Why do it? Because internal heat generation can actually cause increased noise in camera files. The most obvious case I ever encountered with with the Kodak DCS 760 at a Summer swim meet. When I processed the files from that event the early ones were fine and then, progressively, the files got noisier and noise until the camera finally shut down. Even though cameras like the bigger Nikons and the Panasonic GH5 seem to have heat under control I would think that getting rid of the additional heat generated by the battery would improve the life of the electronics while ensuring the more noise free files. It makes sense and it sure couldn't hurt.
Here's the one I bought for the A7ii and the A7Rii:
If $79 buys me assured run time and extra battery capacity I'm all in. Not to mention that the extra hand space actually improves the handling...