We made some improvements in the battle healing skills, here is some information.

Healing without Bandages or First-Aid Kits = 50% effect
Healing with Bandages = 100% effect
Healing with First-Aid Kits = 150% effect

If healing items are available, the skill will spend 1.7 of the item per HP healed.
This applies to skills: Heal Self, Heal Friend, Medic, Heal Squad.

When defending the base all healing will automatically receive the First-Aid Kit bonus without any items being spent (or even required in the Storage), that is the advantage of a base defense.

You can turn on the First-Aid Kit usage for any squad - in the squad edit page. When turned off, the squad will use Bandages, whenever available. Bandages cannot be turned off.