After charging is finished the IC again goes into charging mode every 12 hours for 6 hours even though the battery is connected all that time WITH NO LOAD. According to data sheets, there is no time in a component of the "MCP73837T-FCI/UN" type, so what is the reason for this behavior?
There's much more to know than two lines of text. There may be so many reasons for this bevaviour.
This behaviour may be correct ot not.
It depends on
* schematic
* PCB layout, wiring
* battery age, chemistry, size..
* temperature (change)
* how you detect "charging" state
* and so on...
Every 12h hours sounds like a programmed action. If you are not somehow triggering the recharge action, I would expect it's a featuer of the device, may be it's not correctly configured. Sounds like a question to be asked in a Microchip product support forum.