Why does Turris MOX have RTC battery?

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.