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iPhone 11 Pro Max Battery Cell Replacement

To avoid the dreaded Important Battery Message...

Apple iPhone 11 Pro Max Moderate No estimate Guide 204900

Licensed iFixit integration

This attributed iFixit guide is displayed through Fixonic's recorded commercial API permission. iFixit remains the independent source and author of the procedure.

Guide overview

Before you begin

To avoid the dreaded Important Battery Message caused by using an aftermarket battery in your iPhone, you can instead transplant the battery's BMS, or Battery Management System, from the original battery to a replacement battery cell; i.e., a battery sold without the BMS attached. This guide will show you how to disassemble the old battery and install the BMS onto a new battery cell, restoring the full capacity of the battery while avoiding the error message. Note that the downside to this procedure is that the BMS carries the health information, so even though the battery will effectively be brand new, your phone will still show the original battery health information. On batteries prior to the iPhone 11, you could use a device programmer to reset the health percentage and cycle count, but Apple decided they didn't want people doing that any more, and started encrypting the information such that it can no longer be reprogrammed.

Step 1

Disassemble the old battery

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Start out by removing the tape covering the BMS.

Step 2

Remove the mylar tape

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Open the flaps on the sides.

Step 3

Repair step

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Flip the battery over and peel the tape off.

Step 4

Remove the protective cover

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Remove the plastic cover.

Step 5

Repair step

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Unwrap the BMS.

Step 6

Repair step

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Unfold the BMS.

Step 7

Repair step

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Finish removing the tape.

Step 8

Repair step

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Flip the battery over; you should be able to see the anode and cathode terminal strips of the battery.

Step 9

Cut the BMS from the battery

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Cut the terminal strips to remove the BMS.
Ceramic scissors are preferred here, but normal scissors can be used if you exercise caution. Under no circumstances should you try to sever both terminals with one cut; doing so will short the terminals and could potentially cause the battery to explode. Instead, cut one terminal at a time, from the side, not across the cell.
Please dispose of the old battery safely and in an ecologically friendly manner.

Step 10

Rebuild the battery

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The new battery cell.

Step 11

Set the BMS in place

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After trimming any excess terminals from the BMS contacts, place the BMS on the battery cell.
Fold the terminal strips over onto the contacts on the BMS.

Step 12

Weld the BMS to the battery cell terminals

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Spot weld the terminals to the BMS.
Trim the excess terminal strips.
Spot welding is by far the preferred method of attaching the terminal strips. However, they can be soldered carefully as long as you minimize the amount of heat transferred from the terminal strips into the battery cell itself.

Step 13

Install the protective cover

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Place the double-sided tape over the BMS.
Peel off the protective paper.
Stick on the plastic cover.

Step 14

The outer covering

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TOOL USED ON THIS STEP Tweezers Referenced by the iFixit guide

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Here's the outer covering sticker.

Step 15

Install the outer covering

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TOOL USED ON THIS STEP Tweezers Referenced by the iFixit guide

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Flip the battery over and place the sticker on the back as shown.
Return to the front side and fold the top over the plastic cover.
Fold up the sides.

Step 16

Repair step

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The battery has been rebuilt.