Battle items = can be used when battling another pokemon to restore hp, return a pokemons status back to normal, or even revive a pokemon who has fallen in battle.
The first item is a potion and the second is a revive, both very helpful!
Here are some important things to consider when trying to figure out which item to use. Using items can make a big difference in whether or not you win. Don't forget one more thing about this game. Other trainers can also use battle items so watch out for that.
Overall, just make sure you come prepared with items. It can get difficult to pass the game without them and makes the game alot more fun.