Faraday Bag Battery Life

In Episode 28 of the Complete Privacy & Security Podcast, Aaron Zar from Silent Pocket challenged us to test battery life while using a Silent Pocket Faraday cage. I did, and these are my results.

Methodology: each evening before bed I would put the phone in the condition I wanted to test. I took a “before” screenshot. Some of these screenshots are not of the lock screen, as you will see further down the page. In the morning I took a screenshot of the lock screen again.

I was consistent in my testing procedure but you will notice I skipped quite a few days. Some nights I simply forgot to put the phone in the bag. Some nights I forgot to get a “before” screenshot, and some mornings I forgot to get an “after” screenshot. And in one instance I was traveling for several days and forgot to pack the Faraday bag.

You will also notice that because the test occurred during my actual hours of sleep, the times vary. For this reason, the most important number for each test is the percentage of battery lost per hour rather than the total battery loss.

The results I have recorded so far are shown below. They are grouped not according to day, but according to what interfaces where running when the test occurred. I have tried to include a control for each group of settings. There are still a couple to tests I need to run, and this post will be updated as those test occur.


Time: 8 hours (8.000 hours)
Battery Loss: 10%
Loss Per Hour: 1.250%

Time: 8 hours, 52 minutes (8.866 hours)
Battery Loss: 19%
Loss Per Hour: 2.142%


I ran the most tests in this configuration because this is how I most typically use my phone.

Time: 7 hours, 47 minutes (7.783 hours)
Battery Loss: 7%
Loss Per Hour: 0.899%

Time: 6 hours, 42 minutes (6.700 hours)
Battery Loss: 16%
Loss Per Hour: 2.388%

Time: 6 hours, 9 minutes (6.150 hours)
Battery Loss: 31%
Loss Per Hour: 5.040%

Time: 7 hours, 32 minutes (7.533 hours)
Battery Loss: 23%
Loss Per Hour: 3.053%


Time: 8 hours, 25 minutes (8.416 hours)
Battery Loss: 10%
Loss Per Hour: 1.188%

Time: 7 hours, 9 minutes (7.150 hours)
Battery Loss: 29%
Loss Per Hour: 4.055%

Time: 7 hours, 52 minutes (7.866 hours)
Battery Loss: 44%
Loss Per Hour: 5.593%


I didn’t expect to see much difference when the phone was in airplane mode. Since no interfaces are running, very little (if anything) should be impacted by the Faraday cage. These results were confirmed, but admittedly this was only a single test of each.

Time: 6 hours, 51 minutes (6.850 hours)
Battery Loss: 7%
Loss Per Hour: 1.021%

Time: 7 hours, 14 minutes (7.233 hours)
Battery Loss: 8%
Loss Per Hour: 1.106%


Though my test isn’t complete, my early conclusion is that using a Faraday bag imposes penalty of 3 to 4 times greater battery loss than not using one (my average for all, excluding the Airplane mode test [specifically excluded because Aaron said this step is not necessary] is 3.711% per hour). I’m not trying to pick a fight with Aaron – rather I am just trying to honestly report what I found.

As I said, the test isn’t complete. I plan to conduct the following: a control for the phone with Cellular, Wi-Fi, and Bluetooth enabled, and tests with the phone in Airplane mode but with Wi-Fi enabled (another way in which I commonly use my phone). If there’s something else you think I should test, let me know!

2 thoughts on “Faraday Bag Battery Life”

  1. I listened to that podcast and recall the comments made on either side of the issue. Just out of curiosity I am wondering if you have ever turned your phone off and checked for battery life loss in the AM. I plan to do this myself but I know there is the theory that an iPhone is never absolutely off because one cannot remove the battery. I always turn my phone off before using my bag on this theory alone. I suspect any battery loss in the off state would support this theory…

    1. I’ll give it a shot. I’m on the road for the next couple of weeks and need my alarm but I’ll get on in when I get the chance. Thanks,


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