In reply to NorthernGrit:
I had a Keiss heated vest and inner gloves when I was regularly commuting on a motorbike in winter.
They were very good and kept me warm in zero and subzero temperatures, provided they were plugged in to the power supply of the bike. Without a power connection the battery only lasted on full power for 30 minutes. I forgot to plug them in once leaving work, thought I'd be OK, but had to stop after the battery ran out to plug them in and warm up.
That was 10 years ago and I'm sure battery life has improved since then.
For a smoke in a shed, I'm sure they would be fine. There is now also a much wider choice of makes and types of clothing.
SD.