Update MacOS on a MacBook with dead battery

Solution 1:

Well baring the obvious and replacing the bad battery you will probably have to install the OS on a different computer and reinstall the hard drive. The Mac power module is not responding that the laptop is connected to AC but responding that the battery is bad. Apple will replace the battery for $199 so keep that in mind while doing any work around.

You can also put this MacBook in USB target mode and run the installer from another Mac to perform the upgrade without fixing the hardware. The battery service there is relatively labor and parts expensive due to the thin assembly, delicate cabling and glue that makes the cells part of the case structure. You’re getting a partial frame replacement when the battery is exchanged for $200 and possibly new top case / keyboard if the cabling or parts don’t fit when it’s out for repair.

Solution 2:

I have finally gotten around this without battery replacement (will do another time, not an option right now):

1. Use Disk Utility to create a second partition
2. Make the second partition a bootable installer
   • follow these instructions http://osxdaily.com/2018/09/29/download-full-macos-mojave-installer/ to download a full installer
   • run a command similar to this (adapt paths) sudo ~/Downloads/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Mojave to turn the new partition (/Volumes/Mojave) into a boot disk
3. Restart the computer while holding 'ALT'-key to choose the start volume
4. Chose the new volume with the installer
5. Follow the usual steps to install the OS. It did not prompt about power connection.