Ares 12 (or LTE version) have an internal backup battery in case of primary power failure.
Starting with firmware version 1.7.0 we have improved battery backup time by optimizing power utilization. Now when the device detects primary power failure, LEDs are also nearly completely off and only the Status LED (yellow) blinks shortly every few seconds (it could be missed in normal daylight).
This is perfectly normal and helps prolong time of Ares when running on backup battery.