I am writing from turkey. I am sharing the R&D results I have done in Turkey in line with the possibilities at my disposal. If your battery is turned off, does not charge, does not turn on, please do not hesitate to ask questions. I can help.
Link is Here Youtube Video Link
What will do happen to battery firmware if I perform a downgrade from .1000 to .900?
Did you faced any problem?
Did the mavic detect any inconsistency and performed a new downgrade also just like as it happens during the upgrade?