Yeah, they can add up quickly, at least for me energy keeps raining down. Shards on the other hand not so much lol. I am going to just dismantle vanguard gear for them since I am not having much luck getting them otherwise.
The nightfall is just tough because of all the shielded enemies. Elder Shanks, multiple captains. They can kill you in two shots or so as well which is just ridiculous sometimes. Even when I had my armor of light up and had my armor and recovery set to the top level they can be I was getting killed easily. It really is best to play hide and seek and take your shots carefully. So really to do it you need to plan ahead with your team and snipe them from afar. That way you can duck into some cover. Also, it is a good idea to go ahead and kill the enemies you can run past. If for nothing more than to get some ammo. Top off if you can. At the boss there are a couple spots you can sit in where he cannot get to you and you can sort of wait him out and take pot shots. One is at the beginning, jump up to that ledge that you drop off. Make sure someone is there to revive anyone killed in that spot. Generally one person can go down and take a shot at the boss and another provides cover from vandals and shanks that might come over. Revive the downed player when they are dealt with. The other spot is up where the sniper sits to the right side of the area facing the priest's cell. You can jump up to that ledge and duck under the platform. From there you can walk to the back under the walkway and you cannot be hit there. You can come out once in a while yo take shots at the boss. He will often walk around up to that platform and try shooting you but he can't hit you. When he gives up a bit he will walk down the ramp and you can shoot him there. Just be careful because the servators and shanks can still hit you when you come out from underneath the walkway. The fight takes a while but with elemental damage he will go down. As was said there is no time limit so you can afford to bring ammo synthesis packs and wait for their cooldown timer to reset when you are empty. Just sit in safety until it is up. Grenades do extra damage too so you can pop out and toss a grenade at the boss or whatever might be there, just aim carefully between the metal pipes of the platform if you decide to hide under there. Warlock sunsinger fusion grenades are great for this since they will try to fly toward the enemy and stick doing bonus damage for sticking too. The boss was taking big damage from them when I could stick him with one.