Oh sorry, I should have said that when I started reading yesterday I checked the battery and it was at full charge as I charged it the day before last. And I only read for my lunchbreak, which was not quite 1 hour.
I don't think it's the battery... otherwise how would it be going through a boot cycle (or half of one) before it gets stuck? Wouldn't it just be frozen onto the same screen?
On a side note, I've been happy with the battery life so haven't felt the need to do the upgrade... doesn't seem to be an option now as it seems quite stuck.