Destroy trigger after a certain time

You could add a reference to the battery GameObject in the Triggering GUI Script:

 var theGuiObject : GUIText;
 var batteryObject : GameObject;         // Don't forget to add the reference in the inspector
 var displayTime = 3.0;
 private var timerActive = false;
 private var timer = 0.0;

 function Start() {
    batteryObject = GameObject.Find("ObjectName");  //replace ObjectName with the actual name of the battery object in the hierarchy view
 }
 
 function OnTriggerEnter (other : Collider) {
     if (!other.CompareTag ("Player")) { // Do nothing if tag is not "Player"
         return;
     }
     if (timerActive) { // Reset timer if player re-enters trigger while the timer's active
         timer = 0.0;
         return;
     }
 
     theGuiObject.enabled = true; // Enable GUIText, wait a while, then disable it
     yield Wait();
     theGuiObject.enabled = false;
     Destroy(batteryObject);      // Destroy the battery object when the GUI text disappears
 }
 
 function Wait () { // A custom WaitForSeconds coroutine that can be reset
     timerActive = true;
     timer = 0.0;
     while (timer < displayTime) {
         timer += Time.deltaTime;        
         yield;
     }
     timerActive = false;
 }

You probably have some HUD or interface in your game attached to a player. I would place the message in the hud and run a function there showing the message.

Also by creating my own game I read its better to hide a gameObject or renderer then to destroy and instantiate again (for pickups like weapons health etc) So you can create a main object (empty) with a trigger and the pickup script. have a child that is the battery.

This is in javascript, I am not familiar enough with c++

First the battery script:

 // Asuming the baterry is a child object of your gameobject with script.
 var battery :GameObject;
 var respawnTime :float = 6.5;
 private var isEnabled :boolean = true;
 // hudscript should be the name of the script that is used for your hud.(caps sensitive).
 private var hudReference :hudscript;
 
 function Start() :void
 {
     // You can add a find function here to assign the battery so you do not need to set it in the inspector.
 }
 
 
 function OnTriggerEnter(thisCollider :Collider) :void
 {
     // Asumming the hud script is on the player gameobject that also has the collider.
     // Again hudscript should be the name of the script containing the hud code.
     if(isEnabled && thisCollider.CompareTag ("Player"))
     {
         hudReference = thisCollider.GetComponent(hudscript);
         isEnabled = false;
         HideBattery();
     }
 }
 
 
 function HideBattery() :IEnumerator
 {
     // Disabling the battery gameobject and all its children
     battery.SetActive(false);
     
     // Send the hud a message that a battery has been found.
     hudReference.BatteryPickup();
 
     // optional respawntime
     yield WaitForSeconds(respawnTime);
     battery.SetActive(true);
     
     // Enable the trigger again now there is a new pickup visible.
     isEnabled = true;
 }

 

You can enable and disable the renderer with:

 battery.renderer.enabled = false;

This would do because the battery probebly has no collision, but I would use SetActive because it disabled the whole object and its children.

The hudscript: (hudscript.js)

 var showBatteryPickup :boolean = false;
 var batteryLabel    :String = " You found a battery";
 // The label could also be a icon shown on the hud that you assign trough the inspector: 
 // var batteryLabel :Texture; 
 
 
 function OnGUI()
 {
     // Shows the label on the hud, the label could be a texture or string
     if(showBatteryPickup)
     {
         GUI.Label (Rect (100, 100, 300, 30), batteryLabel);
     
     }
 }
 
 
 function BatteryPickup() :IEnumerator
 {
     var showTime :float = 2.5;
     showBatteryPickup = true;
     
     yield WaitForSeconds(showTime);
     showBatteryPickup = false;
 }

More info: http://docs.unity3d.com/Documentation/ScriptReference/Renderer.html http://docs.unity3d.com/Documentation/ScriptReference/GUI.Label.html