Re: "Hybrids are affected much more than conventional gas-engined cars because they rely on a warm and fully charged battery to allow the electric motor to provide either supplemental or complete power to the driven wheels to achieve the enviable fuel consumption figures published by the car companies. And we all know what happens to our favourite battery-powered electronics when they’re left in a cold car overnight, right?"
I own a Lexus RX400h and see mileage (kilometreage?) change from 8.1 l/100km to 9.1 l/100km in the winter. This has been consistent over the three summer/winter cycles that I have owned the vehicle. However, I don't need a fully warm or charged battery to get electric assist. I can get full electric assist in the first 30 seconds of driving off, but only for a very brief period, but I don't think it's because the battery is cold. I think the drop in mileage is mostly attributable to the fact that the engine has to run more often to keep the catalytic converter up to temp for emissions reasons and also to keep the coolant hot for cabin climate control. Winter gas is also a factor (but that affects every vehicle, not just hybrids).
Also, high heat is actually worse for a battery than deep cold.