How do NPCs heal our Pokémon?

//ads -- adsterra.com -- native banner
?>
In various Pokémon games, there are scenarios where we come out of a big fight (usually a boss fight) and an NPC heals our Pokémon for us. I know that Pokémon are healed in Pokémon Centers using special machinery, but is there any in-universe explanation to how these NPC can heal them at a seconds notice without any help?
Pictures about "How do NPCs heal our Pokémon?"



Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Puwadon Sang-ngern, Thought Catalog, Monstera, Alena Shekhovtcova