Hybrid Mileage Weather Dependent

Is the mileage of the Hybrid, and most hybrid and electric vehicles, temperature dependent?

As part of my 'experiment' to see how the hybrid would handle, I have returned to my 'old ways' of driving since the weather was warm. It is almost uncomfortable to watch the 'economy' meter swing all the way in either direction as I start faster and brake harder than it would like me to.

So, I was watching the average fuel consumption of the vehicle while the weather was warm, through to now in both local and long distance driving conditions. The mileage, driving the way I am driving, started out at a combined city and highway average of 21.8mpg with the weather above 50F. As the weather fell below 30F, I have noticed the mileage has dropped below 20mpg to about 19.8mpg average.

Once I noticed this, I have altered my driving to more fit the weather conditions in Chicago - a lot of snow and ice recently - and I looked for other causes for the dropping fuel mileage.

1. Being a creature of comfort, I would use the remote start option on the keychain. In cold weather, this starts the engine, turns on the seat heaters, and turns on the heat at high. It bypasses the hybrid portion of the vehicle and uses the engine only until you get in and insert the key into the ignition. Each start will operate the engine for up to 15 minutes and all eight cylinders are on. This eliminates the idling fuel advantage that we found in traffic.

2. I adjusted my driving habits to more match the conditions. Slower starts and slower stops and have watched the mileage improve. Greater distances in driving have also had an impact as the engine appears to operate much much longer after the vehicle is started. This is partly because the engine needs to hit a certain temperature before it starts shutting off when idle.

3. We are looking into the fact that battery capacity drops with temperature. This would explain the location of the battery pack under the rear passenger seat within the cab. Most all battery technology has a temperature limitation. In fact, while researching hybrid and electric vehicles, including the Tesla and the foreign imports, the disclaimers on mileage discuss the operating conditions for the mileage claims. This could explain a lot, especially how some foreign hybrid vehicle owners have questioned the mileage on the sticker at the dealership and their actual mileage. What are the differences between the 'EPA approved testing sites?' Do some manufacturers take advantage of temperature and/or other driving conditions?

I would like to hear your thoughts on this topic. BTW, I am back to over 20mpg by listening to what the truck is telling me.