change variable and Texture2D

hello guys i have create a nightvision script and that i want to make a gui battery(of nightvision machine) after the variable go to 80 or 60 and etc change the texture to another, how i can make that… take a look to my script.

var texture : Texture2D;
var nightVisionON : AudioClip;
var nightVisionOFF : AudioClip;
var isNightVision = false;
var fAlpha : float = 0.5;
var NightVisionLight : GameObject;
var batteryTexture : Texture2D;
var battery100 : Texture2D;
var battery80 : Texture2D;
var battery65 : Texture2D;
var battery50 : Texture2D;
var battery35 : Texture2D;
var battery10 : Texture2D;
var NoBattery : AudioClip;
var timeSpeed : float = 0.5;
var batteryPower : float = 100;
 
function Start()
{
        NightVisionLight.active = false;
}
 
function Update()
{
        
        if(Input.GetKeyDown("g")&&(isNightVision == false))
        {
                isNightVision = true;
				batteryPower = 100;
				audio.PlayOneShot(nightVisionON);
                NightVisionLight.active = true;
        }
        else if(Input.GetKeyDown("g")&&(isNightVision == true))
        {
                isNightVision = false;
				batteryPower = 0;
				audio.PlayOneShot(nightVisionOFF);
                NightVisionLight.active = false;
}
if(batteryPower > 0){
batteryPower -= Time.deltaTime;
}
if(batteryPower <= 1){ 
(isNightVision) = false;
NightVisionLight.active = false;
}
if(batteryPower <= 0.5){ 
(batteryPower) = 99;
}
}
function OnGUI()
{
        if(isNightVision == true)
        {
                colPreviousGUIColor = GUI.color;
                GUI.color = new Color(colPreviousGUIColor.r, colPreviousGUIColor.g, colPreviousGUIColor.b, fAlpha);
                GUI.DrawTexture(Rect(0.0f, 0.0f, Screen.width, Screen.height), texture);

GUI.DrawTexture(Rect(43,Screen.height - 65,314,36), batteryTexture);
if(batteryPower == 80);
renderer.material.mainTexture = battery80;
GUI.EndGroup();
}
}

If I understood correctly, you want to draw a different batteryTexture for each range (10, 35, 50, 65, 80, 100) - am I right? If so, compare the battery charge to the limits, selecting the higher texture until the battery charge falls below the next lower texture limit - like this:

...
function OnGUI()
{
        if(isNightVision == true)
        {
                colPreviousGUIColor = GUI.color;
                GUI.color = new Color(colPreviousGUIColor.r, colPreviousGUIColor.g, colPreviousGUIColor.b, fAlpha);
                GUI.DrawTexture(Rect(0.0f, 0.0f, Screen.width, Screen.height), texture);
                // compare the batteryPower to the limits to select the texture:
                if (batteryPower > 80) // from 80 to 100...
                    batteryTexture = battery100; // select battery100
                else if (batteryPower > 65) // from 65 to 80...
                    batteryTexture = battery80; // select battery80, and so on
                else if (batteryPower > 50)
                    batteryTexture = battery65;
                else if (batteryPower > 35)
                    batteryTexture = battery50;
                else if (batteryPower > 10)
                    batteryTexture = battery35;
                else
                    batteryTexture = battery10;
                // draw the selected texture:
                GUI.DrawTexture(Rect(43,Screen.height - 65,314,36), batteryTexture);
        }
}