Hi, thanks for liking the art style! I'm not really that good on pixel art, so hearing you liked it means a lot!
Actually, you can use the health patch whenever you want! It doesn't have to be in a fight, because you can access the file system program whenever you want and use the files inside. This game also doesn't limit the character's maximum health, so you can keep healing the player. The only limit is the disk space; it only has 64KB space, so the character's health data can't go beyond that!