From Liquipedia Dota 2 Wiki
Gains charges based on visible enemy heroes using spells or abilities nearby.
- Total hp/mana restored (max charges):
- Enemy hero must be visible to gain charges. Does not give charges if their spell was cast from the fog of war.
Most heroes, especially supports and gankers, benefit from this item. However, for carries and some junglers, it is only situational because they often spend much of the early game farming and not being the target of spells.