Why is it so short when the gunzerker can use his for like 2-5 mins i feel it its to short? i may be wrong but thats what i feel 
Because you can chain his infinitely, and his action skill has an i-frame 
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Also, he does have a skill that can increase the duration by a lot, but really, you probably want to cycle through it as quickly as possible for the full heal and the invincibility at the start of RtB.
yh ok im thinking to much about losing it 
Unlike the other VHs, he gets cooldown reduction whenever he gets hit, so it’ll usually be back before you know it.
because when you use it with bloodsplosion, an axe can clear the entire field in one throw.
I personally think either it’s duration too short or the cooldown’s too long for reliable usage without Release the Beast or Blood Trance.
Tbh I asked this at first myself, but really once you reach RtB you don’t want it to last a while anyway. You’d rather have the instant heal on demand via RtB activation than staying in it.
But, if you still want it to last longer, spec into Blood Trance in the Bloodlust tree. Increases it by a certain amount per stack of Bloodlust on activation.