There are a couple of ways in which you can check your beacon's health status.
Offline way - where you need not be in range of the beacon:
On the Beaconstac dashboard under the Beacons tab you can find a list of all your beacons along with their battery status and last seen status. (Note that the battery status shown here is not realtime)
Online way - where you need be in range of the beacon:
Login to your account on the Beaconstac app
Under My Beacons select the beacon whose health and battery level you would like to know
Scroll down to Sensor data to see the battery level, other hardware-related info (updated in real-time)