2011 CT 200h MPG going down slightly.

After having my CT200h for nearly 2 years I have noticed the MPG is starting to go down slightly. Nothing major but noticeable. I usually can average 48-49 mpg in warm months and 46-47 in winter. Now the car is averaging about 44 mpg in winter. I am not driving any differently. I try to maximize the hybrid driving as much as possible. The weather is cold, but not bitterly so. Most days are above freezing in Maryland so far. i use the same gas station to refill. It is a name brand station. I assume the gas is fine unless the blending has somehow changed. I have no idea about that. My car gets serviced regularly by Lexus. Tires are properly inflated, etc.
Wondering if anyone else has an original 2011 model and finding this issue. Could the rechargeable battery be undergoing a slow decline? I am not complaining about 44 mpg as it is still higher than what Lexus advertises the CT200h on the sticker.

2011 CT 200h Premium, Starfire Pearl. 24,000 miles driven in almost 2 years of ownership.