How to index objects

Hi guys, im not sure if this is the correct terminology. But what I am trying to do is.. I have a health bar connected to a tower. When a unit is near it decreases. Works great. But when I have multiple of the same tower on the screen its buggy. I think its because I am using the same variable for both towers. How do I make it so their variables are not shared? I have my code below with comments. It is applied to the "towers" in my game.

 using UnityEngine;
 using System.Collections;
 
 public class Tower : MonoBehaviour
 {
     private int testInt=0;    // Update is called once per frame
 
     public Texture2D selectionHighLight = null; 
     private Vector3 captureBarPos = Vector3.zero;
 
     private static float captureBarLength = 500f;
     private static float maxCaptureBarLength =500f;
     private static float length = 50f;
 
     public bool playerCapture =false;
 
     void Update(){
 
         captureBarPos = Camera.main.WorldToScreenPoint (transform.position);
         print("target is " + captureBarPos.x + " pixels from the left"); 
 
         if(captureBarLength>=0){ //this is the code that captures faster based on amt of units in area
         switch(testInt){
         case 1: captureBarLength-=1;
             break;
         case 2: captureBarLength-=2;
             break;
         case 3: captureBarLength-=3;
             break;
             }
             //test
             if(captureBarLength<3){//just a test to see color change
                 playerCapture=true;
             }else{
                 playerCapture=false;
             }
 
         }
         if (captureBarLength <= maxCaptureBarLength && testInt == 0) { //refill bar when no units around
             captureBarLength+=5;        
         }
         if (playerCapture == true) {
                         renderer.material.color = Color.red; //change color when captured
                 } else {
             renderer.material.color = Color.white;
                 }
 
     }
 
 
     void OnTriggerEnter(Collider col) { //detecting if "unit" is in the area 
             if(col.collider.gameObject.name=="Unit"){
             testInt+=1;
 
             Debug.Log(testInt);
             }
         } 
     void OnTriggerExit(Collider col) { //detecting if "unit" is in the area 
         if(col.collider.gameObject.name=="Unit"){
             testInt-=1;
             Debug.Log(testInt);
         }
 
     }
     private void OnGUI(){
         GUI.DrawTexture(new Rect (captureBarPos.x-30,(Screen.height-captureBarPos.y)-50,length*(captureBarLength/maxCaptureBarLength),5),selectionHighLight);    
     }
 }