Sprites assigned to prefab' script' fields not assigned after launch

Hello everyone. I'm pretty new to Unity. So, I have some 2d object' prefab with its HP (1-6). I also had 6 sprites which display every state with every HP. And I want to programmatically change my object's sprite depending on its HP. I have another object with Image component inside my Object' prefab. I've tried to add 6 fields like so

where I attached my sprites to each field. And I have simple switch inside my code:

 switch (Health)
 {
     case 1:
         cell_image.sprite = energy_1_image;
         break;
     case 2:
         cell_image.sprite = energy_2_image;
         break;
     case 3:
         cell_image.sprite = energy_3_image;
         break;
     case 4:
         cell_image.sprite = energy_4_image;
         break;
     case 5:
         cell_image.sprite = energy_5_image;
         break;
     case 6:
         cell_image.sprite = energy_2_image;
         break;
     default:
         break;
 }

But once I run game my objects have no sprite inside Image component and on the Inspector View in my objects there is following:

What am I doing wrong? Thank you in advance!