i would guess that conserve power is ever on for that long (as per the blaster/scrapper/tanker version) but i am not sure how effective Energy drain is, but i can assure you that conserve power is jsut a quickish boos at tha start or end of a fight (depending on when you activate it) but it takes an age to recharge even 3 sloted.
A lot depends on if you are running hasten or not. I certainly wouldn't try this without hasten 3 slotted.
IMO Conserve Power works best when combined with stamina. CP makes end go down more slowly, stamina makes it recover faster. You should find that if have stamina and you hit CP just before you are out of endurance your bar starts to recover while the power is a ctive. Without stamina is many just stay static.
The complexity increaser is Energy Drain, since this is very situational, it's efficacy dependant on how many mobs you hit with it.
Personally I would take Stamina but consider skipping either CP or ED.
I really should do something about this signature.
I didnt have stamina on my brute until lvl 38 !
You can have a stamina less brute, and rely only on energy drain , but you will need to use a lot of slots on end redux , to make up for the lack of stamina !
I had all my atacks with 2 end redux , shilds with one end redux , even sprint had one end redux :P
I could solo non stop , but on teams its hard to use energy drain , !
Conserve power has a 600s recharge , 3 sloted should be about 300 seconds , and it last 90s.
Swift , healt and stamina , will make your brute life a lot beter , conserve power due to its long recharge will almost never be used !
Its always possible to respec out of 2 less used powers to get the medice poll , the passive EA powers, change travel power to fligh and get Air Sup , get rid of one atack, etc...
3 Slotted CP with 3 slotted hasten can be up for about 37.5% of the time (an average).
I really should do something about this signature.
take both 
stamina and conserve power, run all them toggles
I'm a couple of levels away from lvl 35 and Conserve Power on the Energy Aura set, i was wondering if it was worth respec'in once i get and get rid of the Fitness pool in favour of the Medicine pool as i have no self heal and it would be good to have as back up.
Basically i'm trying to find out if you can run a Brute on Energy Drain and Conserve Power alone.