When connecting rechargeable battery to MMPF0100 and using it as backup for RTC on i.MX6, the charge voltage to battery is 2.5V (default).
That is, battery voltage goes up to 2.5V.
When an external power supply is not connected to a system, RTC needs to work by Battery charged to 2.5V.
However, the operating voltage range of i.MX6 VDD_SNVS_IN is 2.9V-3.3V.
We keep only RTC.
Is really more than 2.9V needed in order to keep RTC?
I think that lower voltage is available in order to keep RTC operation generally.
If it becomes so, since it is necessary to change charge voltage setting to Battery more than 2.9V.