Having switched from Amazon MP3 to Google Play Music, the most annoying omission in Google’s offering is the inability to save music tracks to SD card instead of internal storage.
Since version 5.1 of Play Music the capability is actually there, although the feature has not yet been exposed via the user interface. Here’s a neat trick you can use to switch it on manually.
After Apex Launcher has been installed, fire it up and you’ll see a new and hopefully fairly empty home screen (don’t worry, your existing home screen has not been lost!). Tap and hold on the home screen, select Shortcuts and then Activities.
Scroll down until you come to Google Play Music, then tap on it to expand to a list of activities. Scroll down until you come to .ui.SDCardSelectorActivity, tap on it and you should find a new Google Play icon appear on the Apex home screen.
Tap on this new Google Play icon and you’ll be presented with a ‘Download Storage Location’ dialogue box. Simply tap on ‘SD card’ and you’re done!
You can now uninstall Apex Launcher if you wish.
Although the switch has been made, it only applies to music that you ‘Keep on device’ from now on, so you’ll need to unpin and pin all your previously downloaded albums again to move them to SD card.
I’m guessing Google will expose this new capability in a future update, but for the time being this is a very welcome workaround.
In case you’re interested, the saved files are stored on your SD card in the Android/data/com.google.android.music/files/music folder.