Based on the analysis of the device log file the case in question could be comprehended.Short after the alarm that the battery capacity underran 10%, the device switched off.Power cycling revealed a battery charge level of 0%.Within the next 45 minutes, the battery was recharged again.Further entries were found pointing to an old battery.The battery is required to be replaced every 3 years during service.As the device was manufactured in 2011, the battery pack should have been replaced in 2020 already.In case of a power supply failure or if main power is not connected, the device continues operation using the internal backup batteries without limitation of functionality while a power failure alarm is given.The remaining capacity of the batteries is indicated to the user and additional warnings are given when the residual battery capacity underruns 20% respectively 10%.The ifu describes that with a fully charged battery operation can be continued with the current settings for at least 30 minutes (with an old battery with different characteristics due to the aging process, this time might be noticeably less).With a warning the user is informed that if the batteries are not sufficient charged and a power failure occurs, it may not be possible to continue operation for long enough.It can be concluded that the reported event probably was caused by an used up backup battery in combination with an unplugged mains power connection.In consequence, the battery was fully discharged in a very short time.
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