low FPS when battery is low ( unity android )

i make a simple 2d scene in unity 2017.3.1f1 (only 5 sprite renderer). I realized that when my Android device's battery is under 20 %, the frame rate will be 60 to 30. I did all the optimizations I heard, like:

DynamicBatching, Sprite Atlas , Quality Setting , sprite Texture Comprestion Override for Android And I emphasize that my scene contains only 5 sprite (one background and 4 sprite)

i use Application.targetFrameRate = 60; because if don't , all time The motions are stuttering Whether the battery is over 20% or not.

when the vsync is off, the frame is locked to 30 and when it's turned on, it changes for about half a second between 30 and 60

according to profiler (on my android device) Gfx.WaitForPresent start growing!!! (if you want to say it is GPU bound , i think render time don't grow And scence is very simple)

In all these modes, The motions are stuttering.

I tested two kinds of moves

1: Moving camera in the update method by the following code: Code (CSharp):

 void Update () {
    if(startMvCm){
        if (cam.position.y > EndCm ) {
            cam.Translate(0f,(speedCm*Time.fixedDeltaTime),0);
        } else {
            cam.position = new Vector2(0,EndCm);
            startMvCm = false;
        }
    }
 }

2: An animation of moving an image in canvas (simple UI menu with 5 button) using Animator.

And this low FPS see more in low Battery on my "Huawei Mate 10 Lite"