Pretty easy boss fight compared to previous boss fights.
Hartman teleports, switching between melee attacks and long-range attacks. When his back glows, he’ll either launch tracking spines or a shotgun blast of spines. Keep a decent distance away from him (I stayed up on the control panel section on the right of the room for long periods), and use launch (multi launch if you've got it), with the occasion blast of Surge or whatever weapon form you prefer. After ranged attacks, he’ll teleport near you and stomp or attempt to grab you. Dodge away quickly, as he will grab you if you're too slow and drain your health. If you do get grabbed, just shoot him to break free. He will recover his health from yours.
Once you get his health bar all the way down it'll go dark. Two of the power cubes will have been knocked out, and have to get them back in place. There will be some lighted places still in action, so use these as resting stops to recharge energy. Some enemies will spawn, I'd recommend taking them out from the lighted areas before working on the cubes. Using the seize ability can be useful on some of these enemies, as they provide useful distractions to Hartman while you damage him during light phases.
With the cubes back in you notice a second healthbar. Rinse and repeat and damage him down. When he’s low on health, he may knock out the power cubes out again. Quickly reconnect them or he’ll recover his health.
After every cycle, Hartman will be slightly weaker. He’ll take more damage from your attacks, so even if he fully heals, you’ll still be able to defeat him faster. The trick is just keeping distance, dodging his attacks and keeping the damage going.
Overall a fairly easy boss fight compared to others. His attacks are fairly easy to dodge and with new multi-launch you can deal damage quite quick too.