How to get Secret Shield-Weaver Armor for Invincibility in Horizon Zero Dawn: You must find all 5 Power Cell Locations and bring the Cells to the Ancient Armory.
Doing this unlocks the trophy "Got the Shield-Weaver outfit" (Recovered an ancient technology and put it to use).
The Power Cells are found in mission areas but you can go back and get them later. The missions areas are locked until you reach a certain point in the story. You can still free roam after beating the story and collect everything after the game ending.
To save some time it would be best if you pick them up during the main quests. If you die you must pick them up again, they are not saved instantly (must reach next checkpoint). The power cells have a green icon which makes them easier to spot.
If you have trouble reaching a location there's an easy trick: Hover over the area on the world map and press D-Pad Down to see the different layers. Put a marker by pressing X at the same location as the video shows. Now in Game Settings (press Options-Button) turn on "Waypoint Pathfinding". This makes it so you get a new waypoint every few meters to guide you through buildings. This is especially useful for the second Power Cell on the 12th floor of Maker's End.
If you get them during the story just follow the main quest markers and you'll get to the areas automatically.
Power Cell Locations:
#1 - Area: All Mother (Main Quest: The Womb of the Mountain) - 0:05
It's in a side room on the right side after waking up in the mountain (1st floor). Crouch through the hole in the wall to reach it. If you miss it this area gets locked until beating main quest "The Heart of the Nora" which is at the end of the story.
#2 - Area: Maker's End (Main Quest: Maker's End) - 0:52
At the very top of the tower (12th floor).
#3 - Area: The Grave-Hoard (Main Quest: The Grave Hoard) - 1:52
3rd floor, after solving the ring puzzle to open the locked door. It's behind the locked door, you'll walk right into it. You have to open this door and do the puzzle as part of the story, very easy to locate this one.
#4 - Area: GAIA Prime (Main Quest: The Mountain That Fell) - 3:42
3rd floor, after you go through the first part of the building you'll come outside and have to rapel down. BEFORE you rapel down, jump down to the left on the rocks and it's in the hidden purple area.
#5 - Area: Ruins (Free Roam) - 4:23
These are the ruins from the prologue of the game, where young Aloy fell down. Now that she's grown up, one of the doors can be pried open with the spear. When looking at the map it's on the 1st floor in the purple area at the bottom right corner.
After finding all 5 Power Cell Locations head back to the Ancient Armory Bunker. It's marked as a side quest. Insert the 5 power cells, solve the ring puzzle and take the armor. In inventory open the Shield-Weaver Outfit Treasure Box and equip the armor. This unlocks the trophy.
This armor is extremely powerful and renders you completely invincible until it starts flashing red. It absorbs every type of damage, even falling damage. When it turns red go into cover for a few seconds to make it recharge. You can take quite a lot of damage before it gets red. Makes the game much easier.
Horizon Zero Dawn Trophy Guide & Roadmap: http://www.powerpyx.com/horizon-zero-dawn-trophy-guide-roadmap/
Captured on PS4 PRO in Performance Mode. Thanks to Sony / PlayStation for providing a copy of this game.