I think the batteries fitted to our cars don't like low temperatures - the one on my white GTS died overnight last week after I left it outside. We'd been filming in my garage (my mad car project) until late into the evening, but by the time we'd finished, I was so done in I couldn't face clearing enough room to put it back in. Then it snowed. The following morning there was no chance of moving it, so I left it where it was - but when I tried to start it the next day, it wouldn't even recognise the key fobs. Then the boot wouldn't open (less than 5v in what had been a consistently good battery), so I had to jump it for long enough to open the boot. A quick swap over for another battery, and all seems well...