Seal of might + some green M.I shoulders can net you 80% conversion.
I mentioned Beronath reforged, because I think you might be better off going for some jury rigged build. I don’t like the look of bladearc/devastation battlemage. waaaay too skill point hungry.
If set bonus could give +2 to all arcanist, that would be a good start.
I know about the seal of might, thats why i suggested the conversion on Myth Decree since it was intended for Battle Mage use anyway. The weapon have a range of 36 to 54% conversion and with 2 seal of Might its possible to get full aether to physical conversion. Using MI shoulder to get aether conversion is a no no for me, since its occupied by the Spellscourge Shoulder. The 4 set bonuses is too juicy for me, 8% cdr (combine it with max roll on the set and you got yourself 26% cdr), all those bonuses for Deva. I do agree in your opinion about BA part on the set, i think it should be another cast speed based skill maybe FW (since the set also included shield) or CT idk. Swapping the bonus aspd from Overguard to castspeed is better since the main selling point is Devastation which cast speed based skill.
Regardless, this is an untested, super rough warborn battlemage I whipped up - https://www.grimtools.com/calc/m233Jbq2
I left 2 unspent skill points for arcane will + fighting spirit so you can see the damage values with warborn proc active.
Damage looks promising.
Tbh, I think circle of five dagger should have:
I had an idea before some time to test the Battlemage with the Spellscourge set to test how it performs. Basically should be decent with Aeon and CD. Also OA should allow monster crits. Doubt it will be very quick. But 9:30 mention by Strannik looks too slow to me 
Another idea, Beronath sword+Octavius . Forcewave with a twist!
Impressive i must say, but i have different perspective on BM. A spellcasting warrior that can withstand a lot of punishment while dissing out spell left and right is what i envisioned in this class. I just hate how dual wield is soooo viable with any other class combo in this game while the spellcaster with shield part receive little love hence why im talking about Spellscourge set (a set that include shield for BM). Sry, just my personal opinion.
No, I 100% agree. The biggest problem with the battlemage set is that devastation require 66 skill points to hardcap.
That’s about 1/4 of your skill points gone for 1 skill which can’t do much single target damage.
1H Bladearc also isn’t as powerful as it’s 2H bigger brother.
@nery: What’s your weapon damage? Going for aeon’s severely gimps your %physical damage, which makes it less effective against enemy armor.
1H or DW physical builds thrive with big flat damage, or with DoT.
Also - Beronath FW has been done.
Build is outdated now…RoK should probably be a lot better.
Some random theorycrafting: https://www.grimtools.com/calc/62ay1QD2
Arcanist is actually a decent secondary class here cause you have some ridiculous passive bonuses and nullification. The problem is you can’t afford procs.
It’s the best result that @adoomgod was able to get for battle mage in spellscourge set in Crucible. Sounds like it still needs some buffs.
Sadly it’s the kind of time one can expect from classes without single -RR source. Still I wonder what’s the solution. Probably RR proc or as mentioned by Mad Lee a physical CT build.
Another thought came up about The Spellscourge.
What if I replace the Devastation skill with Albrecht Ray.
Given the conversion already in place, we get a strong “physical sword created by magic.” Leave a bonus to weapon damage (possibly increase), but add a change in mechanics. For the beam to hit as before, only for one purpose.
That is, the point is to make a strong skill for damage in one target. Save the opportunity to use the Albrecht beam with a shield from the set.
Replace the arc blade with a blitz, so we get AOE skill with the necessary physical damage and internal injuries.
Add skill Blind side proc to cut physical resist in -%.
Sorry for the text. I use transliteration. If something is not clear, ask, I will try to answer more accurately.
It wont work without tons of dedicated gear, that doesnt exist. And it doesnt solve the main issue - lack of physical RR. That’s why Spellscourge set has ~10 min clear time, while other builds can have ~7min.
Well in general you also need off-hand for devastation, isn’t it? 
I think it says somewhere in item description that the shield is special? I’ve always just assumed that devastation makes a special exception for spellscourge, but I could be wrong!
Yes, this shield is unique - it works like off-hand for devastation and in theory can work in the same way for AAR.
Yup, that’s totally normal shield 
Btw do you think 1h blade arc can carry BM with just 1 point in Devastation, cause that’s what I will try?
I have doubts regarding this - in campaign it could be Ok but too slow. Even now the fight with Fabius feels long,
Base skill of blade-arc has no flat damage. This means that laceration is your only source of flat phys, and @ 22/12, laceration only gives 178 phys damage.
This means that for bladearc to shine, you need to stack huge amounts of flat damage (i.e. 2H’s)
Note: No skill nodes in BA also has +% phys damage - another limitation.
Still better damage compared to dual physical cadence battle mage with Nex & Ortus. 
I really wish Crate put it on the Myth Decree of Circle of Five, since i think its weird that the weapon have aether damage and no elemental damage yet offering elemental to physical conversion, unlike many other weapon.
Касательно [Decree of the Circle of Five] (https://www.grimtools.com/db/items/12555) , может ему подошла бы активируемая аура (как у перекованного Бероната) для конверсии 100% эфира в физический урон ?
Аура позволит контролировать и использовать орудие для разных сборок.