Expansion

:"Tank" redirects here. For other uses, see Tank (Disambiguation).
An expansion or tank is a form of power-up that increases the amount of ammunition Samus can carry, or her Power Suit's energy levels, or otherwise enhances her abilities.
Expansions are abundant throughout the worlds of the Metroid series. While Samus is never required to collect all expansions in order to complete her missions, doing so can make later confrontations much easier. Recent titles of the series also provide rewards for collecting all expansions.
==Types of expansions==
===Energy===
A notable example of a Power Suit expansion is the Energy Tank. Each Energy Tank collected increases the amount of energy Samus can carry by 100 units and fully restores her energy on the spot. Traditionally, she can carry up to 14 of these. On Hard Mode in Metroid Fusion and Metroid: Zero Mission, an Energy Tank only adds 50 units of energy; Samus must then collect a second to form a full tank.
In Super Metroid and Metroid: Samus Returns, Samus can use Reserve Tanks to store excess energy. In the event that her Power Suit's energy is depleted, the Reserve Tank will automatically replenish her energy by four tanks in Super Metroid, and three in Samus Returns. This can only be used once in an enemy encounter. Energy Reserve Tanks can be acquired in Super Metroid, while in Samus Returns they are unlockable through scanning the Samus, Zero Suit Samus and Samus Aran amiibo. These also unlock Missile and Aeion Reserve Tanks.
Metroid: Other M introduces Energy Parts and E-Recovery Tanks the former also appearing in Metroid Dread. Only a few whole Energy Tanks can be acquired in these two games; the rest have to be assembled through collecting four Energy Parts. This is similar to the decrease in provided energy from Energy Tanks in Zero Mission on Hard Mode difficulty. E-Recovery Tanks increase the amount of energy Samus can recover through Concentration by one tank.
In Metroid: Samus Returns, there are Aeion Tanks that increase Samus's Aeion Gauge by 50 units. Like Energy Tanks, Aeion Tanks fully restore Samus's Aeion. She can collect fifteen of them during the SR-388 incident.
===Ammunition===
By far the most common expansion that can be found is the Missile Expansion, or Missile Tank in the non-Prime games. These appear as floating, sometimes glowing missile pods that increase the Missile Counter, traditionally by 5 units. Exceptions include Metroid II: Return of Samus and Metroid Prime Hunters, which add 10 extra missiles; Other M, which adds 1; Samus Returns, which adds 3; and Dread, which adds 2. Dread also features Missile+ Tanks, which add 10 Missiles. Every game that features the Power Bomb, aside from Other M, also features expansions for it. In Other M, Power Bombs are unleashed by charging a regular Bomb in Morph Ball form.
Super Metroid, Metroid: Zero Mission and Metroid: Samus Returns feature Super Missile Tanks that increase Samus's Super Missiles by 5 (Super), 2 (Zero Mission), or 1 (Samus Returns). This tank does not exist in the Prime series, Metroid Fusion, or Metroid Dread, which instead feature the Super Missile as an upgrade over the regular Missile Launcher, and it uses Missile Ammo; in Other M, Super Missiles serve as charged Missiles, and use 5 Missile Ammo each. In Metroid Prime 3: Corruption, Samus can acquire expansions for her Ship Missile Launcher, allowing her to carry up to eleven Ship Missiles if she collects them all. Corruption contains a reference to an unused expansion for the Ship Grapple Beam, although how it would have worked is unknown.
While most Beams in the Metroid series have infinite ammunition, Metroid Prime 2: Echoes and Hunters feature Beam Ammo and Universal Ammunition (UA) respectively, with the Dark, Light and Annihilator Beams and the six Affinity Weapons functioning through replenishable ammunition. In Echoes, Samus can collect four Beam Ammo Expansions that increase her capacity by 50 units each. In Hunters, UA Expansions increase her capacity by 30 units and Samus can collect 12 of them.
Other M introduces a Charge Meter for the Charge Beam, and Samus begins the game with a slow rate of charging. Six Accel Charges collected throughout the game can shorten the charging time by 0.5 seconds per charge. If Samus collects them all, charging will only take half a second for her. Accel Charges have no effect on the charging rate of Power Bombs or the Paralyzer. In all other games, charging is automatic and the speed cannot be increased or decreased.
===Other===
While not technically expansions, "key" items in the Prime Series are included with expansions in the Inventory. Keys include Chozo Artifacts, Alimbic Artifacts and Octoliths, Dark and Sky Temple Keys, and Energy Cells. With the exception of the latter, Samus is required to collect all of these keys in order to reach the Impact Crater, Oubliette and Sky Temple. Only a certain amount of Energy Cells are required to access the Control Room aboard the G.F.S. Valhalla, and acquire the codes that will allow the Galactic Federation to reach Phaaze.
==Rewards for collecting expansions==
All three games of the original Metroid Prime Trilogy, Metroid: Other M, Metroid: Samus Returns and Metroid Dread provide rewards for collecting percentages of expansions. Most often these are Concept Galleries, unlockable galleries of concept art for the game. In Samus Returns, the Chozo Memories are unlocked by collecting all expansions, with a new memory being unlocked for every 10% of items collected.
==Official Data==
===Metroid Fusion manual===
;ITEMS
:"Several types of power-up items are hidden throughout the space station." 
===Metroid Fusion: The Official Nintendo Player's Guide===
;MAXIMIZE POWER
:"By collecting tanks, you can increase Samus's capacity to hold energy, Missiles and Power Bombs. Every tank contributes to her overall strength."
;TAKE THE TANKS
:"Tanks are important discoveries. Without them, you will not be able to hold your own in difficult situations. Seek out all three types of tanks, but beware of fake tanks that come to life and attack. There are 20 Energy Tanks, 48 Missile Tanks and 32 Power Bomb Tanks scattered throughout the research station."
;OFF THE BEATEN PATH
:"You'll have to use all of Samus's special abilities and explore every area to find tanks. Most tanks are in dangerous dead ends or hidden passages. Identify and break through barriers and enter the station's little known areas. You'll discover a wealth of helpful items. See the Tank Trials section on page 106 for strategies on getting every tank." 
===Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide===
;Power-Ups
:"In addition to the primary upgrades that increase Samus's abilities, there are other power-ups that increase her Energy and ammunition supplies. These are some of the most valued items available, but they're also well hidden. Finding them all will require a lot of exploration and some ingenuity on your part. None of these power-ups is required to finish the game, but finding them all will make the game much easier."
===Metroid Prime 3: Corruption Premiere Edition===
;PICKUPS
:"Pickups are objects that enhance Samus's Varia Suit or Hunter-Class Gunship. These include Missile Expansions, Energy Tanks, Energy Cells, Gunship Missile Expansions, and suit upgrades. There are 100 pickups in all, but not all are required to complete the game. However, if you want to see all three endings, collect all of them."
===Metroid: Zero Mission manual===
;TANKS
:"Hidden within the confines of the fortress on Planet Zebes are several tanks that will greatly aid in Samus's mission."
===Metroid: Other M manual===
;Items
:"Items are hidden in a variety of places. Every item you find will augment Samus' abilities."
===Metroid: Samus Returns manual===
;Items You Can Pick Up
:"These can be found left out in the open or hidden in special places."