Reducing Android power usage I have an Android app that accesses the camera and sends SMS messages. My problem is that the phone will be charged by a battery, so the power usage has to be the minimum.

I realized that the screen consumes most part of the battery. Is there a way to open the camera with the screen blanked? 

I also thought to remove the display, but I read that Android performs a hardware test in the boot. The system will boot without the display?

What other ways to reduce power usage in Android do you recommend me?

Any tip will be very helpful,

Thanks
Displaying blank screen won't help you because Even if you display a blank screen, the screen is still consuming power.I guess you only want to use camera feed in your app and you have the control of your android phone as well, so saving battery is one thing that you can manage only with your app though you can't control the most of the apps although there are are couple of things that might come handy.


Try to use marshmallow which automatically helps you to save memory (if you have control of device).
You can disable wifi network and other connectivity services to save battery (look for code online but every code won't work on every version). 
For wifi ,


WifiManager wifiManager = (WifiManager)this.context.getSystemService(Context.WIFI_SERVICE);
wifiManager.setWifiEnabled(status); // pass false to shut it down 


you can create your own customize rom(cyanogen mod is most popular ) which can be modified just with minimal number of required system apps and platform apps so that there will be less number of app to manage and which automatically lead you to less number of system resources requests hence longer battery 


Hope this will help.Good luck