I doubt there's a max capacity, unless your operating system has a limit, but I have read about people putting 750gb drives in s10's with no problems. You'd be looking for a 2.5 inch sata drive, less than 9mm thick, it's easy to replace. I'd try all your options to repair the computer through the software first, it could be that the operating system became corrupted when the power went out and the drive couldn't finish writing something to the disk. Try the rapid restore function, or windows repair, at worst case you could reformat the drive and try again instead of buying a new drive straight up.
Why, may I ask, were you using it without the battery installed?