Thanks for your advice guys. I've only had it about a month, but bought it refurbished. It's in spanking condition and came with a 90-day warranty (still in date). My only bugbear is that the meter showed 70% the last time I noticed (couple of nights ago?) but then I went to switch on last night and just got the black screen. That said, I never shut it down fully (only entered sleep mode) and I have been using it for a month on one charge. I just wish there were a warning popped up to advise the user to charge the device or something along those lines.
Once again thanks - I'll keep a closer eye on it in future!