Notifications of Low Battery Level Magic Mouse & Keyboard

Once again, I have turned on my iMac (but it could equally apply to my MacBook Pro) to see a notification that the battery on my Magic Mouse is flat. I then checked the keyboard and it is at 4%, with no notification. This keeps happening: why does Apple not provide a notification that the battery level on Magic Mouse or Magic Keyboard is getting low? It's not difficult. They do it for the battery on my iPhone. It is VERY frustrating to come to use the computer and then find that the tools I need to use it are dead.