I beat him a couple days ago -- definitely the hardest boss imo. By comparison, the final boss was a welcome piece of cake.
What worked for me is using a pulse gun in each hand, a Stun Needle on my right shoudler and the pulse blade on my left shoulder to switch out with the pulse gun. The twin pulse guns quickly wear down his pulse armor, and the Needle and blade inflict good damage when he is staggered. The hardest thing though is dodging the huge dual laser beams at the start of phase 2. I found that equipping reverse joint lege helps me get some altitude quickly.
I'm already on chapter 2 in NG+ cause holy crap I love this game -- despite some infuriating bosses that get outdone by subsequent bosses. I don't know if I'll do NG++ for the third ending, but right now I'm having a blast. I destroyed Balteus on first try, it goes to show how powerful I became compared to the early game.