by Simeon » Mon Jan 12, 2015 4:31 pm
Basically this will happen if the chat between the primary A CPU and the battery are not good, then the A CPU tell the B CPU battery invlaid, which throws up the UI you describe.
The new firmware for new batteries, was to get around the fact the newer batteries output lower voltage. The percentage power left is derived based off the voltage, as the battery "goes flat" it's voltage drops. The the new batteries appear flat when they are full. This is a two fold issue because the camera will work for less time, and with "low" battery the firmware will not update.
Given you new Nikon battery is reporting as bad, makes me think that ether a wire is broken somewhere thus breaking the comms, or a solider is to think/thin thus also interfering. Thus it might be a wire issue on the power board you replaced, or possible on the main board also.
I hope this all helps you track the issue down, and understand the nature of that error message.
p.s. questions about the firmware go in the firmware section, not the showcase section.