Sentinel Batteries are an important collectible to find as they unlock different areas of the Fortress of Doom in Doom Eternal. Inside these unlocked areas are things like weapon mods, Sentinel Coins to upgrade your Praetor Suit, unique skins, and more.
You’ll naturally acquire three Sentinel Batteries by completing certain missions on each level, but to get all of the unlocks you’ll need to find the hidden Sentinel Batteries. There are 18 in total and this guide will give you a general idea of where to find them.
18 Cultist Base: Ledge
This one is at the first outside arena, where you fight two Revenants and a pack of zombies in between fiery pillars linked by chains. If you look up the mountain you can see the Battery. To access it, turn toward the cliff face and you’ll see a door with a ledge to the far side.
Jump on the ledge, break the door, then smash the button and you’ll unlock a Grav Lift. Go back to the pillars and walk off a beam on the cliff side where you can see a spot to drop down. At the end of this path is the elevator which leads to the Battery.
17 Cultist Base: After Drawbridge
This one is easy to find. It’s located after walking up the drawbridge just before you reach the quest marker in front of the massive doors in the large hallway. After killing a Cacodemon simply hang a left and follow the path. It’ll be sitting on the floor.
16 Cultist Base: Elevator Ride
While looking for the Super Shotgun you’ll ride an elevator to a floor with two Revenants and some zombies. After killing them you should see a grating that, when followed, will lead to another elevator. Take this one all the way down and exit into a room, if you follow the hallway you’ll find it on the floor.
15 Doom Hunter Base: Under The Pillar
After surviving the first arena battle in this area go to the center of the map. Underneath the first pillar in that central ramp is a breakable floor gate. Underneath this is a small tunnel that takes you to the Battery.
14 Doom Hunter Base: Red Keycard
After grabbing the Red Keycard you’ll see a set of stairs on the right leading down. Just follow these stairs to grab an easy Sentinel Battery. Simple as it gets for this one.
13 Doom Hunter Base: Floating Coffin
Later in the area you’ll see a coffin floating above a cliff. With some careful platforming, use it to get to the next area where you’ll encounter some zombies. Take them down and on the far wall you’ll see a Battery hidden inside a small alcove.
12 Super Gore Nest: Wade In The Waste
Once you’ve acquired the yellow key and are in the process of looking for the red key you’ll find several radioactive pools on the ground with a tunnel guarded by spinning fire. Puzzle your way through this to reach a pillar spitting out fireballs. On the other side is a small sewer tunnel that leads to a Battery.
11 Super Gore Nest: Lava Platforming
This one takes a few steps. It’s found in the Buff Totem area outside with several pools of lava. Follow the platforming path you need to in order to complete the objective Reactivating The Power 1/2. The Battery is inside a destroyed building covered in tentacles and flesh, just before your objective.
10 Super Gore Nest: Slayer Key
To get this Battery you need the Blue Keycard. Go back to the first battle you had in this area and open the Grav Lift with the Keycard, the tornado is above it. Up the lift, follow the path up to the left (you’ll know you’re going the right way when you fight a Spectre). Inside a room with broken windows, you'll find a Slayer Key and The Sentinel Battery.
9 ARC Complex: Slayer Gate
Next to the Slayer Gate is a climbable wall next to a ledge leading to a dark doorway. You can either dash jump to the ledge or use the climbable wall. In either case, once you're on the other side you’ll find the Battery.
8 ARC Complex: Giant Tentacle
Before you try to fire the west turret and after you have destroyed the first giant tentacle, pay attention to your surroundings and you’ll see the battery through a window in a room. Simply walk down the hallway leading to that room and you’ll grab it.
7 Â ARC Complex: Purple Slime
At the bottom of the map you’ll encounter an area with purple slime en route to fire the west turret. There is a stack of crates that you need to use. Break the bottom crate to expose an action button. Punch the button to shove the crates against the fence, then climb the fence and you’ll have the Battery.
6 Mars Core: BFG 9000
This one is easy to miss as you’re en route to get the BFG 9000, and it’s pretty easy to be distracted by this fact. Once you're in the tunnel on your way to get to the BFG 9000, turn immediately around and you’ll see the Battery on a platform behind you.
5 Mars Core: Backtrack
On your way to the escape pod after you’ve fired the cannon and you’re platforming through all sorts of debris there’s a Grav Lift that hurls you past two stone pillars. Once you land turn back and jump across those same pillars to reach this Battery.
4 Mars Core: Lost City
Entering the Lost City of Hebeth, you’ll drop down into the area. Immediately to your right is the Sentinel Battery making it hard to miss. "Hidden" might be a stretch here, but it can be overlooked given Doom Eternal's pacing.
3 Taras Nabad: Post Marauder
After defeating the Marauder you’ll be on a small round platform with a bridge leading away. Left of the bridge, look down the cliff to see a ledge. Drop down to the ledge, break the wall, and inside the secret tunnel is a Battery.
2 Taras Nabad: Kneeling Statue
In the main courtyard with the stained glass windows on the upper level is the statue of a kneeling man, left of the large statue in the center. Breaking this statue will uncover a button that opens a nearby gate. You’ll see a breakable section of the wall beneath a large hanging bell. Use the climbing wall to jump above it and punch the chain holding it up, it’ll crash through the floor to where the Battery is.
1 Taras Nabad: Fallen Titan
Before obtaining the Hilt you’ll come across the corpse of a large Titan. Next to him is a small courtyard near his left hand. In here you'll find the final hidden Sentinel Battery of the game.