It doesn't run without batteries so it would have used it batteries during a power outage but your PC probably just quit.
There's never been any firmware upgrades for the HP-2 so it was a database upgrade, that happens only to the SD card. So when removing its SD card and you power on your scanner you get the exact same message of SD card error? So if the SD card can be programmed successfully from Sentinel in a card reader and the SD card are then seated properly then the SD card interface have somehow broken.