Automatically power on Android when the charger is connected

Question

Is it possible to automatically power on the device once the charger is connected given that the device is initially turned off?

Answer 1

fastboot oem off-mode-charge 0 is the genuine method if your device supports. It's Google's recommended method but not all OEMs/vendors implement the command in bootloader. Or on some devices it's reset on next reboot. If off-mode-charge is disabled, bootloader won't pass androidboot.mode=charger commandline parameter to kernel when charger is inserted, so device boots normally.

Otherwise when ro.bootmode property is set to charger on boot, init doesn't continue the normal boot process. Instead limited number of services are started and charging animation is displayed. So you can instruct init to reboot the device whenever charger mode is detected. Create a new .rc file or edit any existing one:

# /system/etc/init/off_mode_charge.rc
on charger
    setprop sys.powerctl reboot,leaving-off-mode-charging

Or execute reboot binary:

on charger
    exec - -- /system/bin/reboot leaving-off-mode-charging

But if SELinux is enforcing, stock policy may not let init execute /system/bin/reboot. So use Magisk's context (or whatever rooting solution you use):

on charger
    exec u:r:magisk:s0 -- /system/bin/reboot

Don't forget to set permissions on *.rc file (chown 0.0, chmod 0644, chcon u:object_r:system_file:s0).

It's also possible to continue boot process instead of restarting the device by replacing class_start charger with trigger late-init in /init.rc file:

on charger
    #class_start charger
    trigger late-init

Or by setting property sys.boot_from_charger_mode:

on charger
    setprop sys.boot_from_charger_mode 1

• This method should work on all devices irrespective of OEM as it doesn't depend on vendor-specific charging binaries like playlpm, battery_charging, chargeonlymode, zchgd, kpoc_charger and so on.
• Also replacing binaries of important services like healthd - which take care of a lot of things related to battery, storage etc. - is not a good idea. In this case if the service runs both in charger and normal mode, device may get into bootloop.
• On non-System-as-Root devices it's not necessary to modify /system partition (e.g. if you don't want to break dm-verity for OTA updates to work). Simply unpack boot.img and edit /init.rc file in ramdisk.
• Though unnecessary, it's also possible to execute an init.d script from .rc file. For reference see How to run an executable on boot? and How to power off when charger is removed?.

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RELATED:

• Android device load process

Answer 2

The battery charging graphic is displayed by /system/bin/playlpm file on Samsung devices.

If you are root, you can edit this file to:

#!/system/bin/sh
/system/bin/reboot

And be sure to add those permissions to the file:

chmod 0755 /system/bin/playlpm
chown root.shell /system/bin/playlpm

Your device will now boot when plugged

Answer 3

So, there are many ways to do so. The most proper one, as always supported by Google (and more and more by others, e.g. nvidia from nougat) is this fastboot command

fastboot oem off-mode-charge 0

Otherwise, you can either hijack the charging binary (not guaranteed to be possible on all devices, but just requires root) or patch your ramdisk (theoretically universal, but will require an unlocked bootloader).

For the first solution, you'll have to find somewhere in your system partition (usually the bin folder) where the program in charge of the battery animation and all resides. Some common names:

• Motorola: charge_only_mode
• Mediatek: kpoc_charger or ipod
• Htc: chargemon or zchgd
• Samsung: playlpm or lpm
• Sony: chargemon or battery_charging
• Most(?) AOSP-based roms: healthd

Once found, you can just replace it with a script such as that above by IET_DEMO.

Touching the kernel is instead something I don't feel like explaining and recommending if you don't know what you are doing.

Just for the records then, I'd just like to underline that offline charging exists because the boot process is fairly energy intensive, and especially on older phones without even fast charging the power draw from the system could be higher than that on the plug.

Answer 4

Just got this working for ZTE Force (Boost Force, Sprint Force, etc).

I used IET_DEMO's answer, but replaced the file located at /system/bin/battery_charging with this code:

#!/system/bin/sh
/system/bin/reboot

Answer 5

For some older Samsung devices, this can be accomplished through NoMoarPowah!:

NoMoarPowah! can automatically reboot into Android when charging is done. Either when fully charged, or when the battery level reaches 15% and Android has enough juice to run.

You need root and you probably don't want to do it unless you really know what you're doing, since I would expect this to modify important system files.

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It looks like this has been removed from the Play Store, but you can probably find the APK hosted elsewhere. (I don't have a trusted link offhand.)

Answer 6

Kernel is loaded at a later stage in the boot-up process, so any modifications to it would not have any effect for when the device is powered off.

This functionality really depends on each device's hardware, most likely in the bootloader (more knowledgeable editors feel free to correct me.) For example, my Motorola Atrix 4G phone begins booting up when I connect a charger, while my Samsung Galaxy Tab does not - it displays the "Battery Charging" graphic and requires being powered on manually.