Hi Bart and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, it would appear to be a false sensing battery level monitor which then would make it an internal hardware issue. Please click HERE for the block/circuit diagram where the battery detection circuit is shown.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even a soldering iron?
Equally important, could you make use of the repair/Service Manual or at the very least, the schematic diagrams?