If the hardware is still in design stage, the easiest thing to do is choose an RTC with lower backup power draw.
https://support.epson.biz/td/api/doc_check.php?dl=brief_RX6110SAB&lang=en
Try google “world’s lowest power RTC” to find other options. Pay careful attention to what voltage the device cuts out at, as that can impact lifespan. In our measurements, we were able to get 6 months backup at room temperature with 1.5F supercap using the first link above.