To charge the rune you have to kill each of the seven named majors that spawn via the small black floating orbs found on the dreadnaught, These majors spawn on rotation throughout the week, a different one every day mon - sun. You must kill one very day of the week to get it charged, [spoiler]if someone has a charged rune you can help them in the rune event which spawns all seven of the named majors thus charging your rune, you may then open the chest or save the rune for when your friend has an in charged rune so he may get it charged quickly to then hold on to it till you get a new uncharged rune[/spoiler]