Charging problem Error 1 and 17

This Roomba S9 tried to collect dog pooh from a carpet. It was a mess. The vacuum was replaced with a new one and this S9 has been put in a box. I recently got hold of it (from an attic), opened and cleaned everything. All parts that needed replacement was replaced and I have 2 original iRobot batteries. But, I keep on getting the message:

charging problem - please install / replace with iRobot battery - error 1 or 17

I even bought a new "3rd party" battery to see if the completely dead iRobot batteries could be the problem - but I get the same message

• cleaned and tested contacts, tested supply cable, soft reboot via buttons, hard reboot via app
• even contacted Roomba directly, told them the history, and they replied: sorry, we cannot fix it, here is a list of latest products - buy a new one.

Is this an error message that is now stuck in a loop in the Roomba? I would hate to throw this away as all the hardware is still good - I am sure there must be a way of getting this block out of the way?