Wait until update-manger opens to present you with updates, then reboot while on battery power. When you log in, you will get update-manager auto-open minimised, but you will also get a dialog that says:

    Running on Battery
    Your system is running on battery. Are you sure wish to continue?
                                                                        [ Cancel ] [ Continue ]

which is not minimised.

Note that it does not say anything about updates, so it is not clear what operation it is asking you about.

<https:/ /wiki.ubuntu. com/SoftwareUpd ateHandling# alert>: "The secondary text for the alert should consist of one or more list items, depending on the exact situation ... Whenever the computer is running on battery, there should be an item (fixing bug 484249 and bug 494772) with exactly the same battery icon as the power status menu is currently using for the battery, and the text: “It’s safer to connect the computer to AC power before installing.” (fixing bug 426708)."