This is an extremely powerful ability, and should be used whenever possible. It can only be used when Enraged, so you may want to use abilities such as [Berserker Rage] to Enrage yourself if an Enrage buff isn't already on. With no cooldown it makes it an easy ability to use in a rotation, if you keep Enrage effects up.
Patch 9.0.1(2020-10-13): Now learned at level 12. Cooldown reset moved to Rank 2 (Level 27) and its chance reduced to 20%. Second charge moved to Rank 3 (Level 42).
Patch 8.0.1(2018-07-17): No longer requires [Enrage], instead having an 8 second cooldown. Now has 2 charges, generates 12 Rage and has a 25% chance to reset its cooldown.
Hotfix (2016-09-23):Raging Blow damage increased by 5%.
Patch 7.0.3(2016-07-19): No longer has charges. Now generates 5 Rage instead of costing 10.
Hotfix (2014-10-17):Damage has been reduced by 17%.
Hotfix (2013-09-23):Raging Blow's damage has been increased by 20%.
Hotfix (2012-09-20):Raging Blow now does 190% weapon damage (down from 215%),
Patch 5.0.4(2012-08-28): Weapon damage increased from 100% to 215%. Now cost 10 Rage, down from 20. No longer has a cooldown. Can be used in any stance and has a maximum of two charges, added by enrage effects. New icon.
Patch 4.0.3a(2010-11-23): Now does 110% weapon damage, down from 150%.