So about that. I grabbed it all before the boss fight expecting that the boss was coming, but instead it was just that wave of regular old nazis. Now there's almost nothing left in the room except that fucker in the cellar throws a shitty 20 point health pack when I get low. Running to get it usually takes away at least 20 health anyways.
I did finally get it just now, though. Dual wielding assault rifles was the answer.
I had the same problem.
Used up all the overcharge help before the nazi waves. Had to fight that boss with 50 health only on Uber difficulty. Fortunately the bar area kind of kept me safe while I sniped his lights. When his chest opened, I just unloaded with the grenade pistol until he died which was only about 4 direct shots. Very rough, but the dog miniboss before gave me so much worse trouble...