How can I tell if hybrid battery needs replacing?
My Prius is getting only 35-40mpg. It was getting 45-50mpg
3 months ago. Is the drop in mileage possibly due to a failing battery?
Colder weather can cause a drop in mileage. The interior heat for your Prius has to come from someplace and I imagine the gasoline engine runs longer to maintain the heat.
Cold weather WILL cause a significant mileage drop. Seen this on my '07 and '10 Prius’s. Drops from 51 summer in my '07 to 44 cold, and 55 summer in my '10 to 47 winter. Happens with all cars, but more noticeable in the Prius due to the mileage displays. Also tire pressures drop 1 pound per every 9 degree temperature drop. Could be a 4-5 pound drop in the winter, and lower tire pressure reduces mileage. Likely your battery is fine. Example: Was getting 45 2 weeks ago with temps in the 20’s. Filled up yesterday with temps in the 45-50 range, and got 56, over a range of 75 miles.