When he charges his AOE ability, have everyone run away for a second. Don't get more than the bare minimum out of range. As soon as he is done casting it (which should be less than one second after you reach a safe distance) run back in along with everyone else. Do not worry about spreading out to reduce the damage from his chain lightning attack - the aura damage is much more deadly.
If you or any of your party members have crummy gear, the healer may find the fight to be damn near impossible. Sucks to be you. It's one of the hardest 5-man heroic fights.