A Sentinel Battery in Doom Eternal is a rare collectible that can found in various levels of the game. Sentinel Batteries have a bright blue glow, which makes them easy to spot. They are usually hidden on ledges or alternative paths.
Sentinel Battery Doom Eternal
Sentinel Batteries can be found in one of two ways. If you haven't encountered a Sentinel Battery on a level, try completing the missions. Each mission has three unique challenges that will reward you with a Sentinel Battery upon completion.
Complete challenges, stock up on the batteries, and open up areas in the Fortress of Doom. To open the rooms, place the batteries into the available slots, and you will be granted access to upgrades within the Slayer's hub.
Once you advance past level three, each level has three challenges to complete. Some challenges are easier than others, so start with the easier ones first. Every level offers new secrets to uncover in DOOM Eternal. This includes a series of items like Toys, Albums, Keys, Cheat Codes, Praetor Suit Points, and the rare Sentinel Batteries. These cosmetic items are hidden and can only be uncovered when you are near them. They appear as a question mark both in the game and on the map, so be on the lookout for them as you progress through the level.