Two weeks ago I was averaging 48 MPG. Suddenly I'm down to 43 average. The culprit appears to be increased charging of the battery system.
Previously, my battery level indicator would drop below 1/2 full before the system started attempting to regularly recharge. Now if I drop one or two notches down from full, the system is constantly applying a minimal charge (one green bar) while maintaining speed.
Can anyone that has had battery pack trouble recall if this was an early symptom?? Or could this be related to climate change (getting cold in the midwest)?
By the way, I bought the car in March 2012 with 32,000 miles. I now have 56,000 miles on it. 110 mile daily commute round trip......

 

It also could be winter gas and it takes longer to get the engine and battery up to operating temperatures. I noticed a much longer lack of IMA in cold weather after the last firmware update.

 

Thanks for the insight. This will be my first winter with this vehicle, and I suspected that maybe the colder temperature affect the battery pack. Although even after an hour of highway cruising the battery pack still does not seem to "warm up".
Is there a way to simply determine what firmware version you have?

 

Only with an HDS attached to the OBDII Port can tell what firmware - If it had been serviced by Honda in the last 24 months it probably was upgraded.

I put the black pipe insulation on my front grill to speed up warming the engine. I have yet to figure out a way to speed up heating the battery.

I have heard that some Canadians put a small space heater in a cookie sheet in low in the back seat to keep the battery at 70 degrees F. I have not done that, I do keep it garaged and have a space heater in the garage to keep it above 55 degrees F. That seems to help.

I have though about the block heater in the engine to keep it warm - I haven't tried that either.

 

All cars suffer decreased MPG in winter. Since you still have an internal combustion engine, you will suffer the same thing. Next summer you should see the numbers pop back up, assuming the battery isn't already losing capacity.