Android Battery Drain issue - How to dig and find the root cause?

Mobile phones is getting more and more powerful silicons and processors, which causes more and more issues on battery management. It is unavoidable to consume more electric power for higher processing power. In this article, I'll investigate and present the basic concept of Android mobile phones and how to dig the battery drain issue. Simple answer that we can find in the internet would be : disable GPS/Location/Bluetooth/WiFi/4G/NFC/etc services, which somehow does not make much sense. You possess the powerful smartphone, and of course you want to maximise the usage of the expensive toy.

1. Screen on
Obviously, screen is the most energy-consuming components of any mobile devices. Longer the screen is on, higher power consumption rate you will see. The only possible way to reduce power consumption for screen-on is to reduce the brightness. Full brightness can consume 7 times more energy than the lowest brightness. Therefore, it is advisable to disable the automatic brightness and adjust it manually not exceeding certain brightness.

2. Screen off / sleep / deep sleep
It is obvious that battery is draining a lot during screen-on. More common issue that caused me chaotic was when my battery drained super fast even when the screen was off. I checked battery stats and all other settings in the system, but the Android built-in battery status doesn't provide much detail. I suspect Google Play Services consumes a lot of battery, but I cannot find what apps use what kind of Services.

For convenience, it is called "sleep mode" when the screen is off. Once the screen is off, the Android system is into sleep mode. Furthermore, if the sleep mode lasts long and no background app is running for certain time, Android is falling into deep-sleep mode. During deep-sleep mode, it uses minimum battery close to 0%.

For most cases, the battery drain issue happens when the phone is only in sleep mode, but cannot fall into the deep sleep mode. Your screen is on for 1~2 hours but the battery lasts only for 8~9 hours, means that some apps repeatedly wake up the phone in sleep mode on the background.

The easiest way to find out how long your phone was sleeping deeply is to use 3rd party battery status app, one of: AccuBattery, GSam Battery Monitor, or BetterBatteryStats (BBS).
Especially, GSam and BBS are very useful to detect which app keeps waking up your Android in sleep mode.

Install one of the 3 battery status apps (just one) and check the deep-sleep time and percentage. If your deep sleep time is 90%+, your battery will last for loooooong time. Above 50% would be normal if you install any social media apps, because they will wake your phone up periodically to check new updates.

3. Wakelock
Wakelock is a proper term in Android used by apps to wake up the mobile. If an app request Wakelock, then Android system will be awake from sleep mode and check whatever the app requested. Therefore, our target to prevent battery draining is how to reduce the number of wakelocks.

If you installed GSam or BBS properly with all permissions given with 'adb' command, it can show the detailed information of Wakelocks. In BBS, check "Partial lock" part to see which apps send Wakelocks. In GSam, go to app usage page and check each app. In the detail page, it shows Wakelock details which tells you what app makes the device awake from sleeping.

Once you found the apps with this method, there are plenty of options you can choose. For advanced users, you can probably set to ignore Wakelock from certain apps, which might cause some issues but increase the battery lasting time. Or, just uninstall the app. Or, disable permission to specific service from the app.

4. My Usecase
First of all, I installed AccuBattery to check overall battery consumption speed. It showed my battery consumption is about 15~30%/hour when screen is on, and 2~3%/hour when screen is off. However, from some time, the battery consumption for battery off increased to 7~8%/hour. I have to find the reason.

I then installed GSam to check the detailed usage of battery by each app, as well as to see which app keeps waking up the system. I found that if GSam and AccuBattery are installed at the same time, they interfere each other which somewhat result in faulty measurement. Basically those battery status apps themselves drain quite large amount of the battery, so it's not a good idea to keep both running.

In GSam, I checked the detailed of Google Play Services, and location service is called excessive number of times. Yes, those general advice is correct, that we have to turn off the location service to save the battery! However, I don't want to loose all the benefits that Google brings to me with the location service. Instead of turning Location Service off, I changed the GPS settings to 'Battery Saving' mode which uses only mobile network and WiFi information without using GPS. With this option, location service will drain much less energy.

Next, I disabled "Ok Google" voice recognition as I seldom use the voice command. Note that if you enable "Ok Google" feature, it always keeps turn on the microphone to detect the voice, which prevents the mobile falling into deep sleep. Maybe better option is to detect your voice only when the screen is on. Anyway, in my case, I disabled even for screen on. (Settings -> Google -> Search, Assistance & Voice -> Voice -> Voice Match)

In fact, there are a lot of settings in Google which can have a big impact on the battery drain. The biggest one would be location services, but other settings should be also carefully reviewed. If you don't think you're using those services, just disable it to save more battery. It's critical part.

Lastly, I found my WeChat also drains quite big amount of energy. Weirdly, it keeps accessing to the step-counter sensor, which should be used only by Google Fit or Samsung Health app. I dig into WeChat settings and found that a feature called "WeChat Run" is enabled. This app-in-app is counting the walking steps and comparing with my friends.I disable this feature, along with other features in the app.

Overall, those internet advice is correct. Disable GPS/Location/etc/etc will save the battery, and my final solution was in fact similar. However, the huge difference in this article is that you KNOW what app makes the battery draining before you disable or uninstall it. As different users have different pattern of mobile usage, it is critical to know what exactly causes the battery issue IN YOUR MOBILE.

For further information, please read these guides and manuals:
https://forum.xda-developers.com/galaxy-s8/help/guide-hunting-wakelocks-battery-drain-t3697324
http://blogger.gsamlabs.com/2011/11/badass-battery-monitor-users-guide.html
https://pdfs.semanticscholar.org/f098/ce049f0d537fac404fd45a58c9f8f4c0bca8.pdf