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I'm working on a research project about Android smartphones power consumption. Using "adb shell dumpsys batterystats" interesting stats can be obtained. For example:

Statistics since last charge: System starts: 0, currently on battery: false
Time on battery: 1h 0m 38s 51ms (99.7%) realtime, 1h 0m 38s 50ms (99.7%) uptime
Time on battery screen off: 30m 21s 169ms (49.9%) realtime, 30m 21s 169ms (49.9%) uptime
Total run time: 1h 0m 47s 207ms realtime, 1h 0m 47s 207ms uptime
Start clock time: 2016-06-18-22-57-54
Screen on: 30m 16s 882ms (49.9%) 1x, Interactive: 30m 16s 367ms (49.9%)
Screen brightnesses:
dark 10s 89ms (0.6%)
light 30m 6s 793ms (99.4%)
....


Estimated power use (mAh):
Capacity: 6700, Computed drain: 298, actual drain: 335-402
Screen: 244
Unaccounted: 36.9 ( )
Uid u0a90: 15.8 ( cpu=15.8 )
Uid 1000: 9.58 ( cpu=9.49 sensor=0.0868 )
.....

As far as I know, the power_profile.xml is used to estimate the power consumption of each hardware component, and differs from device model to another.
Now I have couple of questions:
Q1: How does Android compute actual drain ? I looked everywhere and I can't seem to find an answer. I also checked Android code, but unfortunately I couldn't identify the implementation of the method responsible for "actual drain".
Q2: How Android estimates the screen power consumption ? the Screen's value when its "light = 75%" found in the power_profile.xml on Nexus 9:
ligh: 120.96 ( and it's in mA according to the power_profile.xml)
The report says the power consumption of the screen is 244 mAh, when it was on "light" state for 30 mins, it doesn't make sense to me ! Can you guys explain it ? I tried to check the source code in [here][2], :( again I couldn't find it.
Q3 How accurate these values in the power_profile.xml ? I found on another Android community werbsite some reported issues for Samsung devices. But I don't know about Nexus 9.


Thank you guys for your time.

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I'm definitely not a expert on this but hopefully I can be a little help.

Usually the devices measure the voltage of the battery. When a battery is discharged it gradually degreases it voltage level. When the voltage level is dropped below a certain point the hardware doesn't work anymore. This is one of the reasons why the older ipod/ipad/iphone devices didnt shut down at 0% battery but a lot earlier (If I remember correctly my old ipod touch would shut down around 11%.

EEVblog made a great video about debunking a product that claims that it can extend battery life of electronic products EEvblog Video. Too debunk the product he gives a lot of information about what happens when battery discharges and about when electronic devices shut down.

Hopefully can this information help you a little bit with your project.

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