Pixhawk PDB Calibration Issue


I have an issue with pixhawk PDB’s battery pack detection.
I’ve calibrated the module to detect voltage but not current. I’m using a custom made 4S lithium ion pack for my plane and same time I’m charging it with a solar MPPT (It is a solar UAV).

I confirmed that the battery is getting charged during ground tests. But only few times the mission planner shows the battery capacity increasing because of solar power. But after a while it is continuously decreasing the percentage and falling to battery failsafe mode (below 20% i set).

When I check the battery with another testers, it is showing more capacity and when I connected this same battery at after 2 or 3 minutes, again it showed 85 - 90 %.

Battery is getting charged, but this issue is repeating.

Any ideas or suggestions will be really helpful.