Uff da indeed.
You probably shouldn't have tried to connect the battery with the unit still on, and you definitely should have checked the battery voltage first.
It may be that there is still some power finding its way around the board, but that when it attempts to boot the OS from the microSD, which requires more power, then the board finds itself short and won't start up. Don't know the effects of 'hot-swapping' the microSD as well, that might not be a great idea, either.
Regardless, it does sound from your description very much like you've fried the board, unfortunately.
You probably shouldn't have tried to connect the battery with the unit still on, and you definitely should have checked the battery voltage first.
It may be that there is still some power finding its way around the board, but that when it attempts to boot the OS from the microSD, which requires more power, then the board finds itself short and won't start up. Don't know the effects of 'hot-swapping' the microSD as well, that might not be a great idea, either.
Regardless, it does sound from your description very much like you've fried the board, unfortunately.
