In the new God of War you’ll have to make sure Kratos has a health gauge big enough to survive his battles. For this, you can search Idunn apples, this legendary item helps to increase the maximum health of Kratos in the game. Each time, you will need to collect 3 Idunn apples to increase your character’s life. Know that there are a total of 9 Idunn apples to find in the game, these apples are scattered across all the realms of God of War, and the only method to get them is to open runic chests.
As you travel through the realms of God of War, you will often come across chests mysteriously sealed with magic. You will always see on these chests 3 blue coloured runes. There are several methods to open these closed chests in God of War but in any case you will still need to find the 3 runes to open them. These runes are often placed in the same room as the chest or nearby in the environment of Kratos and Atreus.
You just have to look around you to find the runes that will allow you to open the sealed chest you discovered. Sometimes, it will be necessary to be fast especially for the runes which are engraved on bells. When you have collected 3 apples from Idunn, you will see the message “Increased maximum health” appear on the screen which means that the Kratos health gauge will be permanently increased.