The more features that get packed into each new generation of cameras, the less time batteries seem to last. Things like liveview, gps, WiFi, NFC, VR/IS, and a host of other doohickies just drain them faster than they used to. Even if your camera doesn’t feature superfluous battery draining features, other things can kill them quickly, too. Shooting video or timelapse with long exposures, for example. The obvious choice is simple. Take a bunch of spare batteries. But what if you want more time without having to worry about interrupting your sequence to swap out a battery? That’s where USB power comes in. This video from David at 30Five Millimeter shows you how you can get USB power with your DSLR or mirrorless camera with just a dummy battery and a $5 cable.
Of course, there are commercial USB power solutions available, too, like the TetherTools Case Relay. This is something we use ourselves when we’re filming at shows. At Photokina last year, a 20,000mAh Anker battery managed to last us an entire day shooting video with the Sony A7II. Each night, we just topped it back up to full, ready for the next. But it’s possible to get similar capabilities at a much lower price point. All it requires is a dummy battery, and an inexpensive 5v USB to 9v cable. Do make sure you get one that outputs no more than 9v. A few of those cables go up to 12v, and that will probably fry your camera. While most internal batteries in DSLRs and mirrorless cameras are 7.4v, cameras can usually handle anywhere between 7-9v. Parts List :
USB Power PackDummy Battery5v USB to 9v cable5.5mm barrel adapter (maybe)SmallRig Cheese Plate1/4-20 Cold Shoe AdapterSelf-Adhesive Velcro
The barrel adapter is down there as a maybe as it really depends on which dummy battery you get. Some will already have the appropriate 5.5mm barrel connector. Others, like the Nikon EP-5B (EN-EL15 dummy battery) will have a proprietary plug. And you’re probably going to have to go at it with a pair of scissors and a soldering iron to get the plug you need. Essentially, though, there’s not really much to the whole setup. Insert the dummy battery into the camera. Plug the 9v end of the USB cable into the dummy battery, with an adapter if need be. Then plug the other end into the USB battery and you’re good to go. The SmallRig Cheese Plate, 1/4-20 Cold shoe Adapter and the Velcro is optional but wise. It lets you easily mount the battery on top of your camera, so that you can keep it out of the way.
Skip this bit if you’re not into maths
There is a little issue with the maths in the video, though. In the video, David mentions that he’s using a 10,000mAh Anker battery. He also mentions that the battery in his Panasonic Lumix G85 is 1,200mAh. So, he divides 10,000 by 1,200 to get an answer of 8.33. So, 8.33x more power, right? Well, not exactly. The problem is, that’s 10,000mAh at 3.7v (the voltage of the cell inside the power pack). The Camera’s battery is 1,200 mAh at 7.4v (it’s a 2 cell battery). That means the USB power pack has 37Wh (Watt hours) of total power. The Camera’s battery has a little under 9Wh. So, total power is only a little over four times as much. Not 8.33. When this 37Wh of power is converted to 9v, that means 4,111mAh. And that’s assuming 100% conversion efficiency, which isn’t physically possible. 92% efficiency is usually a pretty good benchmark. And the voltage here is being converted twice. So, 92% of 37Wh to convert 3.7v to 5v is 34.04Wh. 92% of 34.04Wh to convert 5v up to 9v is 31.32Wh. That leaves around 3,500mAh. Still a little under 3x as much power as the original camera battery.
TL;DR the maths
Basically, a 10,000mAh USB power bank is going to give you around 3x the life of a 1,200mAh camera battery. Not 8.33x as suggested in the video. Still, triple the life isn’t to be sniffed at, though. It’s still a great increase over the standard batteries supplied with cameras. And 10,000mAh USB batteries are inexpensive, easy to get hold of, and can be used for so much more than just keeping your camera powered. On any given location shoot, I have at least 6 USB batteries ranging between 8,000mAh and 12,000mAh with me. Always handy for charging phones and tablets, or powering a WiFi router – you can’t beat having your devices connected to each other in the middle of nowhere sometimes. It would be nice to leave the extra DSLR batteries at home and just have everything run off USB. So, I’ve already ordered myself a couple of those USB to 9v cables for my existing dummy batteries. What do you use to prolong your camera’s life when away from power to recharge? Do you just take a bunch of spare camera batteries or do you have another solution?
