We have 2003 Prius with 103K miles-it’s and an all around great car except for a few minor irritations more to do with visability. Question is --we are noticing that the gas mileage indicator is showing generally poorer numbers than previous–we used to get about 43-44 mpg now it is showing more like 32-33. My question is it the gauge or is big battery aging in some way? Any others with this experience and suggestions.
Don’t trust those dashboard MPG meters. You have to do it the old way. Measure miles and divide by gallons used.
My best guess however, is the battery may be getting old. We don’t have enough experience with them to have a really good idea of their life.
Did you change tires? The low rolling resistance tires vs. regular tires can make a difference.
Batteries are over 7 years old and are probably losing their efficiency.
The first item to check is the air cleaner. A dirty one can reduce your mpg. Since you have 103K on the Prius perhaps the air filter is due for replacement. About $10-15 DIY job so worth a shot.