I'm currently trying to track down why my battery on my iPhone 6S is draining at a fast rate and I've been using the Instruments logging on my device to capture logs while normally using my phone. I've noticed a few things in the logs that seem pecular, but I wanted to make sure that I was interpreting the data correcty first before jumping to any conclusions.
Here's what I'm seeing. In the Sleep/Wake state, it looks like over 90% of the time, the device is awake. If I capture live with Instruments instead of logging it offline, it appears to be awake 100% of the time. I've also tried capturing offline and with Instruments the same data on my iPad mini 4 just to get a baseline of what normal looks like (despite the obvious differences in hardware), and it looks like on the iPad it stays 100% awake in both modes.
Here's where things deviate. On the iPad, my Energy Usage level while the device is locked is at 0/20. I never see anything above 0 during the whole run. On the iPhone, however, I see energy usage all over the place. It gets as high as 16/20 in a few places. The entire time, the display is locked, no sound is playing and I've even put the phone into airplane mode. A lot of the time when this is happening, there isn't even any CPU usage being reported.
Here is a screenshot showing high energy usage while pretty much everything is idle. The only difference here is that airplane mode is not on and that this happens to be one of the rare times when the phone is in the sleeping state, yet energy usage is still high.
So the first question I have is that is it normal for iOS devices to stay in the wake state while collecting Instruments data (either directly or offline)? I don't want to spend too much time looking that that if that's expected behavior.
The other question I have is how can I dig a little deeper and find out where the energy usage on the iPhone is coming from? Is there a more in depth view I can use to see what's going on when Instruments says the energy usage is 16/20?