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Borderlands 3 guide: How to increase your inventory

Save your cash for Marcus’ Munitions and SDU upgrades

Gearbox Software/2K Games via Polygon

Your inventory and ammo capacity is pretty limited when you first jump into the world of Pandora in Borderlands 3. Selling every gun you don’t use to earn money and free up space means you’ll be traveling back to a vending machine every few minutes. Also, running out of ammo is a serious problem.

Here’s when you can start upgrading your inventory in Borderlands 3 and how that system works.

If you’re familiar with the Borderlands series, you know that you need to find some Storage Deck Upgrades (SDU) to expand your inventory, increase your grenade count, and increase your ammo reserves. Unfortunately, you’ll need to wait until you get to Sanctuary to buy any upgrades for your character. Just save your money and keep playing.

Play through the first hour or two of Borderlands 3. You’ll complete some tutorial and side missions before finally getting off of Pandora on a giant space ship called Sanctuary.

Once aboard Sanctuary, you’ll get a quest to visit everyone on the ship. If you’re dying to upgrade all of your ammo and storage, Marcus is the man you’re looking for.

When you spawn on the ship, hug the right hallway, pass the golden chest, and he’ll be behind the first door on your right. To the left and the right are vending machines to buy ammo or new guns. But in front of Marcus is a box filled with SDUs. Walk up to the box (pictured above).

Upgrading ammo SDU in Borderlands 3
Borderlands 3’s SDU upgrade box near Marcus on Sanctuary
Gearbox Software/2K Games via Polygon

At the box, you’ll have a number of options. You can buy individual SDUs to upgrade each different ammo type. If you know you’re a big rocket launcher user, you definitely want to invest in some extra ammo. You can also buy upgrades to your bank storage, or the Lost Loot machine — which collects high rarity weapons you miss on the ground.

The most useful SDU upgrades your backpack space. During your time in Borderlands 3, you’ll pick up a lot of guns. If you want to have options or just want to make money by selling back to Marcus, you’re going to need more room in your inventory. Buy as many of these as you can each time you head back to Sanctuary, and then focus on ammo upgrades with your leftover cash.

Each upgrade is more expensive than the last, so be careful not to overspend if you’re trying to save your money for other things.

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