What is the supply voltage range(especially mininum voltage) of a backup battery that RTC circuit can keep the time information?

Autonomous Machines Jetson & Embedded Systems Jetson TX2
1

I can get two information about backup battery voltage range in TX2 module datasheet.

What is the supply voltage range(especially minimum voltage) of a backup battery that RTC circuit can keep the time information?

Ref : Jetson_TX2_TX2i_Module_DataSheet_v1.2.pdf

  1. 2.5 ~ 3.5 V
    3.1 Power Rails
    NOTE:
    VDD_RTC is connected directly to the onboard PMIC. Backup cells must provide a voltage in the range 2.5V to 3.5V.

  2. 1.65 ~ 5.5 V
    6.2 Recommended Operating Conditions
    Parameter Min Typical Max Unit Notes
    VDD_RTC 1.65 5.5 V TX2 / TX2i / TX2 4GB

2

It is 1.65v. The item 1 is the charging setting.