This represents the typical readout I get when doing normal city and sub 45 MPH driving. My “average” MPG on the screen is a little skewed because I do a lot of 85 MPH+ highway driving (and I just replaced 12V battery so stats reset) Is this bad, decent, or good given the age of the battery?
You only drove 9 miles so you can't tell anything from that. You don't say what your normal mix of city/highway is, but around town, you're not going to get high MPGs driving short distances like that. At 10-12 miles you will have only just completed the hybrid warm-up cycle. (More Info: Hybrid Warm-up: 5 modes of Prius Operation.) As far as driving 85+ mph, your economy is going to get exponentially lower for every 1 mph above 60 mph. People report high 30s to low 40s at 70-75 mph.
Calculate the mpg for a few tanks. Or register with Fuelly (or other similar site); it can automate the process.
Before I replaced 12v the screen I shared was pretty representational for around town driving, about 45-52 MPG or thereabouts. I’m getting about 30 MPG at 85-95 MPH which I don’t think is bad at all
