Thanks for the question and the answer. I have been wanted to know that for a while and never asked.

I might disagree with the engining being on most of the time because of faster battery usage. I find it comes on with the heat, and I'm assuming the engine isn't allowed to go below a certain temp or it would loose its low emission status.

Along similar lines, why does the A/C come on by default with heat? I understand for use with the defroster as it can help dry the air, but for normal heating purposes how does it change the air and the energy usage?