Seems that the Texas SNB9024 is the man when we need an RTC. I will try to reach it using the Quark.
3.5 Power management IC (PMIC)
4.13 V_VBAT_BKUP have some instructions about the register to configure the VBAT charging.
Today (23/02/16) I'm giving up from using Intel Edison's MCU for the prototype. I will start using Arduino to make the sensors work. When it get ready, I will see if Intel will have publicated more documentation ou if I need to abandon the internal MCU.
I posted a question on Edison's Forums but until now, nothing helped me. https://communities.intel.com/thread/99031