Bluetooth devices battery energy percentages seem to appear at random at best.
When the Bluetooth icon is clicked on and a list of devices appears; the Magic Keyboard usually but not always shows the energy status as a percentage; with other devices (when turned on) it comes and goes; with at least one the percentage appears briefly only when it is turned off (when the info. is of least value) actually I can no longer recall whether some devices ever showed it but I think so. I noted that the only ones showing it today were under 25% so perhaps it only shows when below a point (but that's not the case for the Keyboard). No settings seem to have any applicability - so the questions are implied.