How long will the battery keep the simulated RTC running

[Prhewett]

I am building a solution that has a need to power down within a few minutes of supply power going off, and then power up when supply power is restored and at 0%.
What I also need in this project is an RTC to keep the Pi on a time close to UTC. In my application the supply power may be off for between 1 and 36 hours.
I see there is a simulated RTC in the PiJuice hat.
Can anyone give me any guidance as to the likely max time the PiJuice battery will keep the simulated RTC ticking over ?

[tvoverbeek]

It uses very little power. I've seen the RTC still running on one of my PiJuices when the power off was more than 2 weeks. So 36 hours would not be a problem (provided there is still some charge in the battery)