Reading the datasheet it appears that the TX1 SOM has an on-board PMIC MAX77620. I am assuming this is a Maxim part but cannot locate a datasheet anywhere for it. Can you provide it?
Reading from the datasheet for the TX1 SOM it sounds like the RTC pin has battery charging capability using the MAX77260. It mentions it can be set from 2.5V to 3.5V and 50uA to 800uA. I plan to use a Rechargeable Lithium Manganese cell size ML-614 on our own custom board but need some details from the MAX77620 to finalize this.