BQ32000: BQ32000 using questions

Part Number: BQ32000

Hi TI FAE,

I have some questions about using BQ32000.

1. According spec, the Vback voltage(Backup supply voltage) < 1.4V, it can't run RTC. But our testing, the Vback voltage < 1.4V, it can keep running RTC until 0.8V. Is it correct?

2. Can I use Pin IRQ which generate 512Hz &1Hz to adjust RTC frequency?

3. My crystal choose EPSON FC135 (https://www.digikey.tw/product-detail/zh/epson/FC-135-32-7680KA-A5/SER4103DKR-ND/6188449), no add crystal. Is it OK?

4. After using a few hours, my find RTC time has some second deviation, is it correct?