|I doubt a new battery will do anything. Generally speaking a bad BIOS flash turns the motherboard into a brick. In the case of a laptop I don't know if the BIOS chip is even removable.|
If this update was advised by Dell I would request help from them.
Is the laptop under warranty?
There may be a method the Dell tech support knows of to re-flash. Possibly using a flash drive or CD.
Do you see anything on the screen at any point?