[mrfunji]

In order for the vehicle to "autostop", a number of criteria have to be met ... most notably engine temperature and transmission temperature. The latter takes longer to warm up, and the colder the ambient temperature is, the more driving it would take.

I don't think the problem had that much to do w/ the high voltage battery, since the engine starter, (really one of the motors in the transmission, powered form the high voltage battery) performed fine (read engine started) in the cold weather ...