[OnePlus 3T Questions & Answers] zaeembutt:
1. Update apps to reduce Android system battery drain.

Sometimes there are no mysterious ways which are killing the battery life in fact these are the common issues. Since 2009 Android system has been designed in such a way that if the apps are not updated then your Android system kills more battery to run the apps better. Android apps must be updated so that Android System does not need any extra effort to run the app most effortlessly. Not updating the app is also the main cause of Android system battery drain.

2. Clear Apps Cache.

This should be the most common practise of every Android user to clear out the cache. If you do not clear the cache so the RAM of your Android device will do some extra effort to find the related data from cache memory. Cache memory is the part of RAM which is first access by the RAM to find data. If you do not clear it then the cache memory will increase the data in it and RAM will use more power to find the respective data. In order to improve Android system battery drain you should clear cache data frequently. Go to Settings > Apps > select app > Storage > Clear cache; to clear all app caches simultaneously, go to Settings > Storage and USB > Cached data > OK.

3. Clear System Cache.

Like clearing the app cache, clearing the system cache is as important as clearing the app cache. You use different apps on daily basis which is stored in RAM so the processor can read it fast. Same like this the system apps that run the OS also stores their data in RAM so that it can be accessed clearly. In order to reduce Android system battery drain you must clear System Cache.

Steps to Clear System Cache.

First press the Power and Volume Down button together until you see the Fast Boot Menu.

Use the volume buttons to navigate and press Power Button to select.

If you see the robot on its back, hold Power and press Volume Up once to access the recovery menu.

Use volume button to select Wipe Cache Partition.

Press power button to confirm.

Reboot your device after clearing the device.

4. Turn of WiFi and GPS location.

It is the most common mistake we do and we ignore. Many Android users does not know that the WiFi option and Location Services are the part of Android System. We keep on looking for solution or apps which kills the battery but we does not know the solution is quite simple. Android system battery drain is mostly caused by 24/7 enabling the WiFi service and Location Service. WiFi is turned on 24/7 will continuously looks for WiFi around you and Location service enabled will do the same and looks for your location. Disable these services when you do not require them which possibly will improve the battery drain.

5. Factory Reset.

If you are still having the issue of Android system battery drain then the last option is Factory Reset. So if you have decided to do factory reset then first you should back up all your data. Make sure all your important data is safe and you have stored it in safe place. So go to Settings and select Backup and Rest option which will reset you Android device. Factory reset will erase every thing you have on your Android device and it may improve Android system battery drain. Some bugs or errors may hide under some files which you cannot access and they continuously kills the battery so doing reset may improve Android system battery drain.