I'm pressuming it was, I was lucky enough to have a spare lying around but I've also read of it on other forums. The only other thing I can think would be your battery isn't handling the cold to well. There's some sort of cold cranking power that batteries have, you can get ones that take the cold better than others. Mine was exactly as you describe though, it was always really sluggish first thing but after that it was great where as now it just cranks no bother. There's a way of testing for current drain with a suitable multimeter, you set it to amps I think then take of the positive battery lead and put one probe on the battery and the other on the battery lead and measure the current draw. If it's really high then I would go alternator as a good suspect but if there's not much then I'd go battery. Another thing you could try is to leave the battery disconnected over night, hook it up in the morning and see if it works better, if it does then the battery must be ok.