The Tether Tools Case Relay is a device that allows you to power any camera, continuously, using ordinary USB battery packs. This could sound like a dream for any videographer or timelapse photographer! However, as any experienced photographer will tell you, aftermarket power solutions can be a nightmare if they aren’t both extremely simple and 100% reliable. So, how does the Case Relay actually perform in the field? You’re about to find out!

Unlimited, Constant Camera Power?

I took a complete Case Relay kit on a 1,300 mile California road trip and shot a few hundred gigabytes of raw timelapse imagery and video footage. The Tether Tools kit that I brought with me included the $99.99 Case Relay device, a $34.99 camera battery adapter, a $49.99 10,000 mAh USB battery, and a nifty tripod leg “handy contraption” that runs $18.95, all for a grand total of about $204. That may sound like a lot, but it’s actually LESS than the price of four Canon LP-E6N or Nikon EN-EL15a batteries. Heck, it’s exactly $30 cheaper than just three Sony NP-FZ100 (A7Riii or A7iii) batteries!

For those of you who already have your own USB batteries (Anker, etc.) and plan to just gaff-tape your stuff to your tripod leg like a “MacGyver of photography”, …you’ll only be spending $99.99 for the Case Relay and $29-45 for a camera battery adapter. (This is known as a “dummy” battery, in case you already have one of those, too.)

Here’s the bottom line: What do you get for the $99 investment in the Case Relay? You get that thing which is so desirable in power solutions for electronic devices: simplicity and reliability!

There are other external power solutions out there, most of which cost about the same. However, what you simply can’t find anywhere else is the hot-swappable capability which means you never have to stop rolling on your video or put a blip in your timelapse shooting, while you change batteries. For many types of shooters, this is going to be an incredible benefit, one that is worth every penny.

By the way, before we continue, and speaking of “other external power solutions”, if you’re interested in powering other devices such as a laptop, charging camera batteries, and also multiple USB devices such as cell phones …then the device you need to check out is Tether Tools’ recently announced ONsite power system, which you can check out HERE.

Alright, now on to our Case Relay review!

Nikon D750, Venus Optics Laowa 12mm f/2.8 Zero-D
1/15 sec @ f/16 & ISO 100

How The Case Relay System Works

Here’s how the Case Relay System works: all USB batteries output 5-volt power through a USB cable. The Case Relay unit itself takes that USB power and charges its own internal, 1,300 mAh, 7.4-volt battery. It is this battery that actually supplies power to the camera.

Most DSLR and mirrorless cameras require ~7.4 volts, (not 5) so the Case Relay effectively ensures that the camera always has enough power to stay on, even while you unplug the main USB 5V battery and plug in a new one.

For those of you electronics geeks, here’s the obvious caveat: Because of the 5V standard that USB batteries have, you’re not necessarily going to see an exact conversion of mAh (Milliamp Hours) from the USB battery’s rating to that of an OEM camera battery.

Say, for example, you have a 10,000 mAh USB battery, and you’re using it to power a camera that normally uses ~2,000 mAh batteries. Are you going to get exactly FIVE camera batteries worth of power out of the USB battery? No, but you could get about 2-3 internal batteries worth of power, which is not bad in terms of electricity efficiency.



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For those who are wondering, the Tether Tools brand USB battery, the Rock Solid external battery pack, is a 2-cell Lithium Polymer battery, which means it is 3.7V x2 = 7.4V. So, the only bottleneck is the USB cable itself, which the Rock Solid USB battery regulates from 7.4 down to ~5V.

I wish there was a way to safely put 7.4v straight through from a battery to a camera, but so far there are very few ways to do this, and some of them could literally explode, (don’t ask!) …while others cost just as much as the Case Relay, yet aren’t hot-swappable.

Simply put, the Case Relay system is unique in its capability, and a great value for the investment if you need what it offers.

Nikon D750, Rokinon 20mm f/1.8
1/100 sec @ f/11 & ISO 100

Real-World Shooting Experience

In the field, the Case Relay is a simple system to set up and work with, and also to keep track of in general. On one end of the Case Relay you attach the camera “dummy” battery, and on the other end, you attach any USB battery. You’re good to go

Officially, the best order in which to plug things in is this: First, remove your normal camera battery, and replace it with the “camera coupler battery” or dummy battery. Then, take the Case Relay and connect it to your USB battery. If it’s a USB battery that needs to be turned on, turn it on so that it starts giving power to the Case Relay.

Unofficially, sometimes I like to plug the Case Relay into the USB battery for a minute or two first, just to make sure that the Case Relay device is, in fact, charging up. Because if the Case Relay is low on power to begin with, your camera will notice, and I simply prefer to have my camera’s internal battery always think that it’s at least at 50%…



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The Case Relay is simple to set up and works smoothly for both photo and video applications. Overall, the build quality and durability of both the USB battery and the Case Relay feels superb. It’s also fun to “flick” the USB battery to get it to turn on.

Here are my official test results: I was able to shoot back-to-back nightscape timelapse exposures of 30 seconds for at least 8 hours straight, on a single 10,000 mAh battery. Swap that out with a ~$39 Anker 20,000 mAh battery, and you’ve got days (or literally a whole 24 hours, uninterrupted, if you need) worth of timelapse photography in a relatively portable and affordable system.


Nikon D750, Rokinon 20mm f/1.8
10 sec @ f/2.8 & ISO 1600

In video shooting, with the Rock Solid 10,000 mAh battery I was able to get more hours than I could test when shooting 1080p video, with my LCD brightness turned down since I was usually shooting in dim lighting conditions. I imagine you could get through almost any long day of videography with just a single 10,000 mAh battery, with another 10,000 mAh battery as a backup just in case.

When shooting 4K video, (on a Nikon D850) I recorded over 4 hrs of video footage, (that’s a lot of gigabytes!) and I still had enough battery power left to charge up my phone too. That’s another beautiful thing about the Case Relay- you don’t have to carry around multiple battery solutions anymore, for charging all your different devices. Not only can you both charge your phone and power camera, (at the same time, if your USB battery has two ports like the Rock Solid pack has) …you can also buy other accessories (available on Amazon and elsewhere) to charge literally any type of battery through this 5V power supply.

Nikon D750, Venus Optics Laowa 12mm f/2.8 Zero-D
30 sec. @ f/8 & ISO 3200


I won’t hold it against the Case Relay that there isn’t a way to put 7.4V straight from the battery to the camera and get closer to the expected mAh worth of life out of a 7.4v battery pack. The USB protocol itself simply isn’t capable of doing more than 5V. And, it is the ubiquitousness of USB battery packs themselves that makes this solution so great!

I will say, however, that it can be unsettling when the camera itself starts to think that its dummy battery (the Case Relay) is getting low. The way the Case Relay works, it fluctuates between 60% and 85% charged, or the green and orange LED lights. So, the camera itself may never think that its battery is 100% full. (Most cameras these days have not only a “3/4/5 bars remaining” type meter, but also a menu option to display the exact %% of battery capacity left.)

So while it doesn’t actually stop you from shooting continuously, it can be a bit unnerving. The camera’s own battery %% meter seems to want to fluctuate between 20% and 60%, on my Nikon D850 and D750.

Also, it doesn’t seem to matter whether the Case Relay’s light is green or orange, I’ve seen the Case Relay LED light be green while the camera thinks its power source is at 25%, and I’ve seen the Case Relay be orange yet the camera thinks its power source is at 60%.

At the end of the day, however, all that matters is that I can keep shooting!

Of all the long-term endurance tests that I performed, there was one time when the camera did think it had died even though the Case Relay and USB battery still had a bit of juice left in them. However, I’m going to blame that on Nikon being much more picky about its voltage input; this problem would probably not arise on Canon cameras which seem to be willing to operate smoothly even if the voltage drops briefly. From what I hear, Sony cameras can be hit or miss, depending on how demanding you are of the camera. (Using IBIS and recording 4K video, for example, has got to put a significant draw on the battery power!)

The other situation which could be frustrating is this: If you have the type of USB battery pack that needs to be turned on, and will auto-shutoff quickly when power is not being drawn from it for a minute, then the Case Relay unit might lose power permanently if it gets full, stops asking the USB battery for power, and yet can’t “wake” the USB battery again when it needs to start charging again.

For this reason, I recommend using USB batteries that are essentially always on, or always ready to give power whenever a USB device “asks for it”. (Most Anker batteries work this way, and of course, so does the Tether Tools Rock Solid battery.)

Overall, here’s my final word on the Case Relay’s reliability: considering that every camera determines its remaining battery power differently, (usually by measuring the voltage it is receiving) …I strongly recommend testing the Case Relay as soon as you get it, with all of your USB battery packs, just in case your specific camera has a problem, or if one of your USB batteries doesn’t play nice with serving up its power on demand.

Nikon D750, Sigma 14mm f/1.8 Art
2 sec @ f/1.8 & ISO 3200

Who Should Buy The Case Relay

This system is designed specifically to help you shoot all day, without stopping. Whether you need to actually shoot un-interrupted for 5-10 hours or more, or you just need to be able to keep rolling on your video clips, the Case Relay is well worth the investment.

If you’re the type of photographer who has no problem lugging around 4-5 “normal” batteries and stopping your shooting periodically to swap them out, then you might not think you need what the Case Relay offers. Then again, if you’re the type of photographer who prefers to stick with name-brand batteries, the Case Relay solution could actually be much more affordable! Especially for anyone who may already have one or two USB batteries laying around, with 10,000 or 20,000+ worth of 5V power!

(By the way, after 15+ years of trying various generic batteries and having almost all of them wind up dying (permanently) after just a few months or a few thousand clicks, I do highly recommend sticking with name-brand batteries. Not only are they more likely to stand the test of time, but they’re also unlikely to explode in your camera, as I have heard in some generic battery horror stories.)

Hands-down, if you’re into timelapse or video, you should consider this solution. It can also be useful for all-day, hands-free operation for things like shooting commercial work in a tethered situation, or even a photo booth at a party or wedding reception.

The only caveat is, there are certain newer Sony cameras that can be plugged directly into a USB power bank, while also keeping their battery in the camera, thus allowing you to achieve your own “UPS” (Uninterrupted Power Supply) effectively. Unfortunately, in my experience, these solutions do still wear down the internal battery slowly if you are recording 4K video and/or using IBIS.

Nikon D750, Nikon 70-200 f/2.8 VR II
1/125 sec @ f/5.6 & ISO 100


Nikon D750, Nikon 70-200mm f/2.8 VR II
1/100 sec @ f/8 & ISO 100


The Tether Tools Case Relay is a product that I’ve been hoping could exist for many years now, and as soon as it was released I knew I wanted to review it someday. To be honest, I was afraid that it simply wouldn’t work reliably, or that it wouldn’t even use USB power efficiently. So, it was great to finally get it out on an adventure and put it through its paces, and it was even more exciting to find how seamlessly it worked, and how much camera power it offered! I think the Case Relay is absolutely worth the investment.

You can purchase the Tether Tools Case Relay on B&H here, or through the Tether Tools website.