Hi,
I suggest looking into the respective IC charge profile. Battery voltage threshold (VBATT) is nominal value of what IC will charge battery up to.
Batt regulation voltage can be configured to specific battery you want to use. As the battery depletes, If Vbatt voltage is below 2.6V battery threshold range, the IC implements trickle charging.
For your application - Please look into MP2623 and MP2633
Best,
Nouman