Steam Deck Battery Disconnection

Introduction

Prerequisite-only guide! This guide is part of another procedure and is not meant to be used alone.

Use this guide to safely disconnect the battery before beginning repairs on a Steam Deck.

Turn on your Steam Deck and allow the battery to discharge below 25% before starting your repairs, as a charged lithium-ion polymer battery can be dangerous if accidentally punctured.
As an extra precaution, Valve recommends putting your Steam Deck into battery storage mode within the BIOS before starting any internal repairs. Read how to do that here.
Power down your Steam Deck and unplug any cables.
If you have a microSD card installed, make sure to remove it before opening the Steam Deck. If you attempt to remove the back cover with it still installed, it could snap right in half.
During your repair, it can be helpful at times to lay the Steam Deck face-down into its case to protect the thumbsticks and prevent wobble.

Tool used on this step:

FixMat

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Use a Phillips driver to remove the eight screws securing the back cover:
Four coarse thread 9.5 mm-long screws
Four fine thread 5.8 mm-long screws
Despite the standards, Phillips screwdrivers can vary in size and shape—two drivers labeled as the same size may fit differently in the same screw. Use the size that fits the snuggest into the screw head.
Throughout this repair, keep track of each screw and make sure it goes back exactly where it came from to avoid damaging your Steam Deck.

Insert an opening pick into the thin gap between the back cover and the front shell, along the edge of the right grip.
If you're having trouble inserting your pick at the grip seam, try starting at either the top or bottom long edges first, then slide the pick towards the grip.
Pry up on the back cover to release it from the locking clips.

Once the clips are disconnected from one edge, the rest disconnect easily.
Grip the back cover at the opening you just created and pull it up and away from the device to unclip the long edges.
Remove the back cover.

Tool used on this step:

Tweezers

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If you have a refreshed Steam Deck version with the black motherboard cover, skip this step.
Use a pair of tweezers to remove the piece of foil tape covering the hidden screw on the board shield.
If possible, try not to rip or tear this tape so it can be reused. If necessary, you can fashion a replacement by cutting a piece of aluminum foil tape to fit.

Use a Phillips driver to remove the three screws securing the board shield:
One 3.4 mm screw
Two 3.7 mm screws
Only the two 3.7 mm screws along the left edge are present in refreshed Steam Decks.

Remove the board shield.
Depending on the age of your Steam Deck, this shield may stick to the thermal pads underneath.
During reassembly, ensure that the fan cable lays on the side of the board shield and isn't pinched underneath.

Grip the battery cable by its pull tab and pull it directly away from the motherboard to disconnect it.
Alternatively, use the flat end of a spudger or a clean fingernail to gently push the connector out of its socket, then disconnect it completely by hand.