I think it's a combination of being a bit older and the fact that I now ride more in the Winter than when I was younger as I played footie through the Winter and with three kids riding time was limited, one advantage of being a bit older is more time and too old to chase a ball around a football pitch. I called into a bike clothing shop in Bournemouth on my way back today and they said they wouldn't stock battery powered versions as don't get warm enough for long enough. Despite their advice I think I'm going to try Lithium battery powered Oxford 'vest' as think I only want an hour or two of warmth later in the day and a couple of my bikes won't power accessories, I'll probably end up wishing I had listened to the advice!!