I have a hunch that the wiring from the battery to the KIB panel may be the issue though since all level sensors and the battery indicator are faulty, and you have replaced the panel. Could be two bad panels, but unlikely. As a check, I would run a test wire from the 12 VDC battery directly to the KIB panel and see if you continue to have problems. If the problem is not resolved, I would measure the resistance from the individual tanks at the panel wiring. The level sensors operate on a basic voltage divider circuit:
I would measure the resistance of the level tank wires to ground at the panel (after disconnecting the wires from the panel) as the tanks fill. That will separate whether the problem is at the panel or in the wiring, resistor pack or sensors.