I was just talking to someone who is driving one of the test a plug-in Priuses. He has had it about a week. Apparently he was adivsed that if the temperature was below zero not to charge the battery and if the temp was -20F do not drive the vehicle at all. Why? Is this bad for the battery or the car? Being in Maine we can get temps well below zero in the winter. With the thermal management system in the Volt, is this a concern? I was surprised to hear this.