The Turris MOX does not keep time when mains power is removed despite having an RTC battery. The time is always reset to 2001-01-01. What is the purpose of the battery then?
That’s re-iteration of this thread, right? DNSSEC not working due to NTP not working and vice versa
I believe RTC is exactly the purpose of the battery and thus something is wrong in your particular case, but I’m personally not confident about these HW details.