Battery failure is signalized by rotation of the signal strength indicator as shown below:

This might happen if your batteries have more then 2 years, or that there is some kind of battery problem.
To check batteries and solve battery life issue:
SMS solution (Only for EasyGates PRO with firmware 18.x.x)
Check batteries with SMS EG INF 12345, you will receive SMS where you will see this information: EXP:0 Time to battery change (days): https://wiki.2n.cz/egum/latest/en/4-funkce-a-uziti/4-7-funkce-pro-lifty
Put new batteries into the gateway 4x AA NIMH.
- Send SMS with counter reset, parameter 60, confirmation with password: EG CNF 12345 60 = 12345.
Analogue phone connected to the FXS port solution:
- Try to change batteries.
- Reset with the analogue phone connected to the FXS port by dialing 12345*60*12345* the counter for battery expiration.