Just bought a 07 Prius and since than have driven it 250 KM and done a bit of a research. Here is what i have to share:
I have driven it around 250 Km in the last 4 days, and it is giving me 22.6 km/l average. As far as I have researched the health of batteries can be judged from the mileage you get. if you are getting any where between 20-25 KM/L you donot need to worry for at least another 200K In sha Allah.
More over I have got hold of the Prius owner's manual in English you can download it from:
(click or copy paste in your browser, it is a pdf file)
Lastly, My prius was kissing every speed breaker in Lahore when loaded with 3 or more passengers, Just had packing installed (1 inch front/ 1.5 inch back shocks), the problem is resolved. Got them installed from the kharadia next to Filter house on Montgomery road lahore. charged me Rs2,800 (bargain with him, he asks for 3,000) Also thinking of installing 175/75/15 tires (currently has 65's) that should add about another inch to the clearance.
Hope the info helps.
Tip: One thing I read from the manual is that you should never leave you car shifted to (N) as the batteries only get charged when the gear knob is in (P)(D) or (B). If left in (N) for long the batteries might get drained out and the car might not start.