Endurance Charges?

How do Endurance Charges work? Are they crucial for a higher level melee marauder? Thanks!

You gain endurance charges by using Enduring Cry or Warlords Mark, but Enduring Cry is the most efficient way.

Endurance charges give you 5% physical resistance and 5% elemental resistance each, and it works additively on your existing resistances.

It is absolutely crucial for high level melee characters in general.

I would run +3 max charges on the passive tree, and pick the +1 max charge from quest, therefore having 7 max endurance charges. The benefits are too big to ignore.

Does anyone know if getting 2x gives you 2 more endurance charges?

From a YouTube video I saw recently - I would say yes you get 2 more.