Some models of satellite trackers are equipped with a battery voltage reading instrument.
The voltage is monitored every minute and is displayed in the popup along with the other parameters (Lat / Long etc ..) that you get by clicking on the boat icon.
When the voltage is less than or equal to 11 v. a notification is sent to the APP and email (if it has been registered in your profile).
The notification is repeated every 12 hours if the voltage remains below 11 v.