The fastest way to upgrade your carrying capacity in Borderlands 4 is to hunt for specific collectibles and complete open-world activities scattered across Chyros. These reward you with SDU (Storage Deck Upgrade) currency, which is spent exclusively on increasing your backpack size, ammo reserves, bank space, and lost loot machine capacity. Forget random drops; this is about targeted exploration.
There are five primary sources for earning SDUs: finding glowing Vault Symbols, defending hacked Propaganda Speakers, solving Evocarium puzzles, reactivating Ancient Crawlers, and discovering hidden Survivalist Caches. Each activity offers a fixed SDU reward upon completion, making them a reliable way to strengthen your Vault Hunter for the long haul. Prioritizing these activities early on is the single most important thing you can do to avoid the constant frustration of a full inventory and empty magazines.
What Exactly Are SDUs and Why Are They Critical?
Storage Deck Upgrades, or SDUs, are a permanent character progression system separate from your level and skill trees. Accessed from your main menu, the SDU screen presents a list of categories you can invest in: backpack inventory slots, bank storage slots, lost loot machine capacity, and individual ammo capacities for every weapon type in the game (pistols, SMGs, shotguns, etc.).
Each purchase increases the cost of the next upgrade in that same category, so while your first few backpack upgrades might be cheap, the tenth will require a significant amount of SDU. This system forces you to make choices. Do you become a generalist, spreading SDUs evenly across all ammo types? Or do you specialize, pouring everything into making your backpack enormous and maxing out the ammo for your favorite Ripper SMG?
This is not a minor quality-of-life feature; it is fundamental to your power curve. More backpack space means less time spent sorting loot in the middle of a firefight and more opportunities to haul valuable gear back to a vendor. More ammo means you can sustain damage output during Chyros's lengthiest boss battles without scrambling for scarce ammo drops. Neglecting your SDUs is a guaranteed way to hamstring your own progress.
Where to Find Every SDU Collectible and Activity
The open world of Chyros is dense with icons, but a few are more important than others for your inventory management. As you explore, keep an eye out for the map markers corresponding to these five activities. Completing all of them in a given region is a key part of clearing the map and building a powerful character.
Hacking Propaganda Speakers
These activities are combat-focused challenges. You'll find large speaker panels, usually in fortified enemy positions. Interacting with one initiates a hack sequence with your robot companion, Echo 4. As soon as the hack begins, you must defend the speaker from several waves of enemies.
A progress meter appears on your HUD, and it only fills when you are within a certain radius of the speaker. If you're downed or pushed too far away from the objective, the progress will stall. The goal is to survive the onslaught until the meter reaches 100%. Upon successful defense, the speaker will broadcast some new, less-hostile messaging, and you'll be immediately rewarded with a chunk of SDU.
Borderlands 4 in-game screenshot
Solving Evocarium Puzzles
Evocariums offer a break from combat, testing your observation and platforming skills instead. These take the form of ancient-looking stone structures or technological pylons. Interacting with the central Evocarium device will release three glowing orbs of energy that shoot off into the immediate vicinity.
Your task is to find and collect all three orbs. They are never far, but they are often cleverly hidden or placed in hard-to-reach spots, requiring you to use your jetpack, mantling abilities, and the environment to reach them. One might be on top of a tall ruin, another tucked away inside a cave, and a third hovering over a precarious jump. Once you've gathered all three orbs, return to the Evocarium to deposit the energy and claim your SDU reward. These are often some of the quickest SDUs you can earn if you have a sharp eye.
Borderlands 4 in-game screenshot
Finding Vault Symbols
The most straightforward collectible, Vault Symbols are a returning feature for series veterans. These are iconic, bright orange symbols painted or carved onto surfaces throughout the world. They are often hidden just out of sight—around a blind corner, on the ceiling of a cave, or behind a piece of destructible debris.
There's no puzzle or combat associated with them. Simply walk up and interact with the symbol to 'discover' it. The game will register the find, and you'll get a small but welcome SDU deposit. Because they are often located near major points of interest or along the critical path of main story missions, you'll find many just by playing the game thoroughly.
Activating Ancient Crawlers
These are massive, derelict mobile fortresses that now serve as mini-dungeons. To complete an Ancient Crawler, you must first locate a missing power cell somewhere on or around the structure. Once you have it, you must carry it to a designated power socket elsewhere on the crawler.
This sounds simple, but the crawlers are teeming with hostile creatures and bandits. Furthermore, carrying the power cell often restricts your movement or ability to fight, turning the journey into a tense escort mission where you are the package. Successfully inserting the power cell will reactivate a part of the crawler, revealing a loot chest and rewarding you with SDUs and a unique cosmetic item.
Locating Survivalist Caches
Think of these as the ultimate treasure chests. Survivalist Caches are large, distinct weapon crates hidden exceptionally well within the environment. They don't appear on your map until you're very close, encouraging pure, unguided exploration.
Finding one requires a different mindset. You need to think vertically, check behind waterfalls, and look for small, unmarked cave entrances. Your reward for this diligence is substantial: a cache always contains a bounty of high-rarity gear (guns, shields, mods) and a very generous amount of SDU. They provide the biggest single SDU payout of any of the activities listed here, making them a top priority whenever you're in a new area.
How Should You Spend Your First SDUs?
With SDUs being a finite resource, a smart spending strategy in the early game will pay massive dividends later. While it's tempting to immediately boost the ammo for your shiny new legendary, a more structured approach is far more effective.
Follow this priority list for your first dozen hours on Chyros:
- Backpack Space: Your absolute first priority. Every single SDU you earn should go into backpack upgrades until you have at least 30-40 slots. This drastically reduces the number of times you have to pause the action to drop or sell gear.
- Lost Loot Machine: After your backpack feels comfortable, invest a few upgrades here. This machine, located at your home base, automatically collects any high-rarity (blue or higher) gear you fail to pick up. A bigger capacity means more chances to recover a legendary you missed in the chaos.
- Primary Weapon Ammo: By now, you should have a feel for your preferred weapon type. Start sinking SDUs into the ammo capacity for that gun (e.g., SMG or Shotgun). Don't worry about other weapon types yet.
- Bank Storage: Midway through the game, you'll start finding gear that's perfect for another character or a different build. This is the time to start expanding your bank storage, allowing you to save that gear for later instead of selling it.
By following this order, you create a smooth loot and combat loop, ensuring you're never forced to abandon good gear or run dry on your go-to weapon during a critical fight.
Borderlands 4 in-game screenshot
Final Take
Don't treat SDU collection as a chore to be saved for the endgame. Weave it into your natural exploration of Chyros from the very beginning. Every Propaganda Speaker you shut down or Evocarium you solve is a direct, permanent investment in your own power and convenience. A bigger backpack and deeper ammo reserves will make every other aspect of Borderlands 4—from boss fights to loot farming—a more enjoyable experience. Get hunting.