Need help with Enabling/Disabling GUITextures with script

My script is for a flash light, the idea is that when the variable energy goes below 50 the GUI of a green battery disappears. The issue I am having is that my script doesn't work with the drainspeed variable, the GUI doesn't disappear when it's drained below 50, however i wonder if this is an issue with the function only being read once...

 var lightSource : Light; //Connect the light source in the Inspector
 var bat1 : GUITexture;
 static var energy : float = 60; //The energy amount of the flashlight
 static var turnedOn : boolean = false; //Boolean to check whether it's turned on or off
 private var drainSpeed : float = 10.0; //The speed that the energy is drained
  
 function Update () {
     if (Input.GetKeyDown(KeyCode.E)) ToggleFlashlight();
 }
  
 //When the player press F we toggle the flashlight on and off
 function ToggleFlashlight () {
     turnedOn=!turnedOn;
     if (turnedOn && energy>0) {
        TurnOnAndDrainEnergy();
     } else {
        lightSource.enabled = false;
     }
 }
  
 //When the flashlight is turned on we enter a while loop which drains the energy
 function TurnOnAndDrainEnergy () {
     lightSource.enabled = true;
     while (turnedOn && energy>0) {
        energy -= drainSpeed*Time.deltaTime;
        yield;
     }
     lightSource.enabled = false;
 }
  
 //This is called from outside the script to alter the amount of energy
 static function AlterEnergy (amount : int) {
     energy = Mathf.Clamp(energy+amount, 0, 100);
 }
 
 function Start(){
 
 if(energy > 50){
 bat1.enabled = true;
 }
 if(energy <50){
 bat1.enabled = false;
 }}

and this is my script