DOOM Eternal is all about beating, burning, blasting, and bludgeoning every demonic creature you come across. While the early creatures you face are pushovers, DOOM Eternal ramps up the difficulty quickly. Because of this, you’ll want to acquire all the upgrades in the Fortress of DOOM right away. This is done via Sentinel Batteries, which are used to open the doors in Doom Slayer’s base.
You can acquire Sentinel Batteries by either finding them in a level or completing mission challenges. Given how critical these are for obtaining new upgrades, you’ll always want to explore and hunt for them. Enhancing Doomguy’s abilities will make some of the later missions much easier – especially once the game starts throwing Super Heavy Demons at you. On the map, Sentinel Batteries are marked by a lightning bolt and they glow blue in-game.
The other way for gathering them is via mission challenges, which unlock a couple hours into DOOM Eternal. These are side objectives that ask you to either kill enemies in a specific way or find collectibles. Some challenges include igniting enemies on fire, destroying specific weak points, or completing the timed trials. You should always try to complete mission objectives since most of them are easy and only require you to change your playstyle a little bit.
Once you have some Sentinel Batteries, you can insert them in the battery slots throughout the Fortress of DOOM. We recommend picking up the Weapon Attachments and increasing your ammo, health, or armor. These are some of the most beneficial in the early game and on harder difficulties.