Hi Rohit,
The VBAT pin on the CC85xx is a pin for battery voltage monitoring, and should be connected directly to the battery voltage via a resistor which is chosen carefully. If you go into the Power Management panel in the PPW Configurator you see a section at the bottom called Battery Voltage Monitoring. Select enabled with external resistor of. Then you can change the resistor value, and observe that the range which you are able to meassure changes. For example for 100kOhm the range is:
Lowest measureable voltage is in the range 2.08 to 2.69 V
Highest measureable voltage is in the range 3.65 to 4.91 V
Further down in the panel you see that you can set up thresholds for automatic power down, low battery LED warning etc. For 100kOhm resistor value all these thresholds should be set between 2.69 and 3.65V (because of the range windows above). If you want to have the tresholds set lower (because of the battery you are using) you should lower the resistor value. For example a 47kOhm resistor will let you meassure voltages in the range 1.64 to 2.08 V.
The BQ25015 is both a battery charger and a DC-DC converter. The output voltage is on SW (pin 19). This voltage is changed with the resistor network and can be in the range: 0.7V - Vbat.
-Kristoffer