2015 MacBook Pro OS

MacBoy27 wrote:

Excellent.. thank you for the info.

How can I instal Monterey on an external drive whilst still having Mojave on my Mac? I would have thought that when I turn on the laptop it would go and boot from the Mojave as its already on the machine?

If you have multiple startup volumes, there are two ways to select which one to start up from.'

• Use the Startup Disk control panel in System Preferences to choose a default startup drive. I believe that is what it would be called in Mojave, and perhaps also in Monterey. Apple shuffled things around in Ventura: on my machine, System Preferences is called System Settings, and the Startup Disk controls are buried within the General control panel. But wherever it is in Mojave and in Monterey, it will be there.
• When powering up or resetting the Mac, hold down the Option (⌥) or Alt key. On Intel-based Macs, this will bring up the Startup Manager and let you select a different startup volume at boot time.

Reference: Mac startup key combinations - Apple Support

What would be the process for Installing Monterey on an external drive, then getting the Mac to boot from it and also install updates on my machine as it still has Mojave in its system?

For a clean install:

Format the external drive using the GUID partition scheme, and the APFS (non-case-sensitive) filesystem. Then when you run the Monterey installer, there should be a screen asking where you want to install the system. Just pick the external drive.

If you like, once you have Monterey on the external drive and have booted from that drive, you can run Migration Assistant, using the internal drive as the startup disk from which to "migrate".

Or:

Format the external drive using the GUID partition scheme, and the APFS (non-case-sensitive) filesystem. Then clone your Mojave drive to it, using Carbon Copy Cloner or SuperDuper! After checking that the backup worked, and that the external drive is bootable, install Monterey "in place" on the external drive, over top of Mojave.

Last but not least.. today I replaced the M.B internal battery pack as the existing one had inflated like a balloon.. no wonder the Mac seemed to get through a charge pretty quickly !!

The process is quite delicate and laborious and took about 1.30 hours and lots of foul language...but I don't give up easily. 100% success!!

It's good that you got rid of the swollen battery pack. When lithium batteries go bad, they become a fire hazard.

2015 Macs still support the the Startup Manager with the Option key. As long as a properly installed boot volume is installed on internal or external drives or partitions, the Startup Manager will show it.

You need to be running Sierra, High Sierra, Mojave, Catalina, or Big Sur on the machine installing Monterey on the external drive. Donwload Monterey from

How to download and install macOS - Apple Support

And run the installer on the drive you want to use as a boot drive. Keep in mind the startup manager may see the volume when Sierra or earlier systems do not because a solid state or flash drive has to take APFS formatting on Monterey.

Use more than one version of macOS on Mac - Apple Support

"f you install a compatible macOS on an additional internal or external storage volume, your Mac can start up from either volume."

While creating an "additional internal … volume" is an option, I'd suggest going with the external one.

If you look at the structure of a Monterey startup drive in Disk Utility, you'll find that what looks like a single startup volume in the Finder is not a single volume on the drive. For security reasons, Apple has carved off some "read-only" operating system stuff, put that into a cryptographically-signed sealed system volume, and further hardened the system by running off of an APFS snapshot of the sealed volume.

Why make the structure of your internal drive even more complicated by having two systems on it?

MacBoy27 wrote:

When you say to install Monterey 'somewhere', the only place I can install Monterey would be on my external third party 1Tb SSD... but if you say Monterey will not install on a 'non Apple' SSD then how can I trick Monterey to install itself on the third party external SSD?...

My understanding is that the Monterey installation will fail if

• It thinks your firmware needs updating (e.g., no previous successful installation of Monterey), and
• You have a non-Apple SSD installed inside of your Mac

The Monterey installer is happy to update your firmware if the SSD installed inside of your Mac is an Apple one – even if the drive on which you are installing Monterey itself is an external, non-Apple one. Or so I've gathered by reading other posts in this forum.

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This aside, I would urge you to create at least one bootable external drive, and set it aside, before doing surgery on your Mac (or having a shop do the surgery for you). You'll need to boot from something (an external drive or Internet Recovery) to initialize the new internal SSD, load macOS onto it, and restore your data. With old Macs, I would suggest not putting all of your eggs into the Internet Recovery basket.

And of course, prior to the upgrade, back up your data …

Take it in to an authorized service center to upgrade your internal storage. You really want 256 GB minimum for newer OSes.

Also Catalina and newer OSes only support 64 bit applications. Make sure you have updated drivers and applications for use with it. You can also install a newer OS on an external drive. You may need to remove applications that are taking up space on your internal drive to run the installer for the newer OS.

https://freemacsoft.net/appcleaner/ is a great utility for removing applications. If you have the original images (DMG) files from your downloads for these applications and licensed emails, copy that info to an external flash drive before using appcleaner to remove the app. The app removes all files associated with any given app.

I believe that you can get larger internal SSDs for that machine. One possible source:

Other World Computing – OWC Solid State Drives For MacBook Pro with Retina Display (Late 2013 - Mid 2015)

However, do not install a third-party SSD (or pay a repair shop to install one) until after you've installed Monterey somewhere. From what I've read in other threads, the Monterey installer checks if your Mac's firmware needs an update. If it does, the installer then checks to see if you have an Apple SSD before installing that update. If your internal SSD is a non-Apple SSD, the firmware update fails and the Monterey installation fails.

Once you have installed Monterey somewhere, and your firmware is up to date (as far as Monterey is concerned), you can reportedly swap in a third-party SSD and install Monterey on that SSD all day long.

The OWC site fails to mention this – although it does refer to the need to upgrade to at least High Sierra (to ensure that the Mac will be able to recognize the SSD at all).

As for the battery replacement, you know what I have to go through as a certified Apple tech. Definitely not for the faint at heart. And static electricity and risk of sharp objects with the battery need to be avoided. For anyone ill experienced at working inside a notebook computer, I just recommend taking to another certified tech.

MacBoy27 wrote:

Thank you again for all the suggestions... I have another option that I was considering.

In order to make space on my existing drive, if I deleted all my documents folder (After copying them on to an external drive and backing up my machine!) that would give me enough space to install the Monterey update on my machine, once done would I be able to use my last backup to restore files or would that not be feasible?

If your internal drive holds only 128 GB and space is so tight that you cannot even install a new version of macOS without deleting files, I wouldn't count on being able to do the upgrade and put all of your data files back onto the internal drive afterwards.

You need to keep some space free on a SSD, or the machine may have a difficult time hiding all the overhead that is involved in managing the remaining free space (and dealing with inherent SSD rewrite penalties).

Another question, how do I reset the 'battery charging' record on the Mac now that I have replaced the battery pack?

I don't know.