Can I display the mouse battery level on my desktop permanently?

You may be able to view the battery status of a wireless Bluetooth mouse and keyboard

from within (or linked through) the Bluetooth icon which can be made to appear in Finder

main window upper right side. Both items should be a little faster to view, via this path,

than going into System Preferences> Keyboard, Mouse, etc.

Haven't see a third-party application or widget that could show the battery life remaining

in the computer or in an iDevice's external BT wireless peripherals. There may be one.

A widget by name iStat Pro used to offer a means to see these items, but not in the last

version, and the company who made the original great one, no longer exists as such.

Good luck & happy computing! 🙂

There is a small app known as Mighty Monitor which sits in your dashboard and can thereby be viewed at a click.

Here is the link. https://www.apple.com/downloads/dashboard/status/mightymonitor.html

Note: OS X will provide ample on screen warnings when the battery levels get low. Constant monitoring shouldn't be necessary.

This software was known to me when I posted above, however the maker's site

appeared to be not fully updated as to what supported OS X it works with now.

The monitor software is a dashboard widget, according to the maker site:

• Mighty Monitor 5 (support to Mavericks 10.9) may/not be OK for El Capitan 10.11

http://www.starmerville.com/mm/mightymonitor/Mighty_Monitor.html

{When I get some kind of wireless mouses (other than those furry kind that seek out

heat and food in winter) I may try the software to see if it works out. My Mac Mini

Late 2012 i7 server still runs Mavericks 10.9.5, from one of two built-in 1-TB HDDs.

Had considered partitioning both drives to have four 500GB for experimenting; but

didn't get feedback on how older OS X in hardware would react to firmware update.}

So without additional software, I suggested the immediately possible. 😐

Yes, I happen to have it and use it. It meets my needs adequately, but I believe it was updated and not having need for that I haven't checked it further.