DIY: Shoe mount USB battery with cold shoe attachment

DIY: Shoe mount USB battery with cold shoe attachment

A number of Sony cameras (And cameras from other manufacturers) can now be both powered and charged via an external USB source. With the short battery life of my Sony A7s II that I use for shooting events, I wanted to find a convenient way to extend the time between battery changes.

I have several small (and large) USB batteries and I have a few different methods for mounting them when working. The method I’d like to share with you today is one of my favorites for “running and gunning.”

To build this you’ll need these items:

You may also need some heat shrink, some gaff tape, and perhaps some loctite as I’ll mention.

The build is simple and quick, it should only take a few minutes to piece it together.

Place one stainless steel clamp around the USB battery, you will likely need to wrap some heat shrink or gaff tape around the middle of the battery to allow the clamp to close tightly. The Aukey battery will fit snuggly without this step.

I recommend test fitting the battery on your camera to find the best place to mount it. For me, it’s roughly centered. The big thing is to make sure you can still access all the controls with it in place. Be aware of where the USB port on both the battery and camera are when you fit it together.

Once you’re happy with the clamp’s position, you’ll want to take the Shoe to 1/4-20 adapter and push it through the hole in the clamp. You will need to apply pressure on the clamp (holding it closed) to get the screw through. Leave one of the nuts from the 1/4-20 adapter on, remove the other. Now take your standard 1/4-20 nut from the hardware store or Amazon and use it to tighten the clamp to the adapter.

If you only want to mount the battery, then you’re good to go.

However, I think it’s nice to still be able to mount a shotgun microphone or something lighweight like that, so I also added a shoe mount to the battery so I could still use a Rode VideoMic Pro or similar microphone on the camera while using the battery.

To do this, take another cable clamp and flip it the other way around. Install it close to the first clamp. Once you’ve gotten that in place, you’ll need a 1/4-20 bolt. Thread that through the clamp and into the bottom of the shoe mount.

You’ll need to straighten everything out and make sure it’s level before tightening it down completely.

I recommend using a 1/4-20 nylon threaded nut to prevent the nut from backing off. You may also use loctite blue (removable) to help keep everything in place and keep it from spinning around.

To further the “professional” image, you can place heat shrink around the clamps prior to putting everything together.

The finished product is very lightweight and will dramatically increase the time between batteries on your Sony camera.

Results

I have not done a purely scientific test yet, however, I did do a quick test of battery life with and without the USB battery. Without the USB battery, the camera lasted around 1 hour 15 minutes before it died on a fully charged battery. The second test I did with a battery that read 99% at the beginning of the test and it died around 2 hours 30 minutes. The USB battery was still in the “Green” portion of it’s charge when the camera died.

Why did the camera still die when the USB battery was still fully charged? Well, USB power is a bit of a lie (at least on the A7s II). In reality, it just extends the run time of the primary battery. Probably because the camera cannot convert 5V to the 7.4ish volts the camera requires without generating a bunch of heat. So, in effect, it really just extends the life of your primary battery. Basically doubling the life.

As a side note, if you turn off your camera at any point during your shooting, the USB battery will begin charging the main camera battery. So, in theory, by simply switching off the camera from time to time you’d not only save some power throughout your shoot but you’d also get a little more of the power out of the USB before needing to swap the main camera battery.

In fact, I did a quick test with a USB power meter and this is what I found:

  • With camera ON, the A7s II draws 0.5 amp (give or take a few mA).
  • With the camera OFF, the a7s II draws a max of 1 amp (if the battery is not 100% charged).
  • In other words, you can charge a battery faster than you can keep a battery alive :-D.
  • Also: This means you don’t need a battery with more than 1amp of output (unless you want to try the DC-to-DC coupler option).

 

I didn’t have the time to test, but I would imagine that you could run through two, possibly three Sony batteries before even this small USB battery would be tapped out. That means you can record 4-6 hours with 3 sony batteries.

Other Options

For those who have a full rig, will be shooting from sticks, or don’t mind some extra bulk…. you could use a DC-to-DC coupler which will allow you to use a USB battery of any size to actually run the camera, as described here.

You could also pick up the sony battery grip. The downside to that is it’s expensive and it will be very unlikely to work with the next camera you buy.

 

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