There is a US government study here:
http://www1.eere.energy.gov/vehiclesandfuels/avta/publications/ld_librar
y.html

Look at the Toyota entries.

Also search Google for "Prius fleet" for other studies.

GOOD LUCK!
Bob Wilson

A FEW batteries have given out before 200K. Most Priuses, incl. the
Vancouver Taxi fleet are getting over 200K. Jesse Rudowsky had 330K on
his original battery when the car was totalled.

You got a long way to go, unless you had the very first batteries,
which, IIRC had some problems.

Batteries whould last ten years.  Toyota has only replaed the ones here in
accidents.  However, we have put money asidewhne the day arrives, as it will
toa $3,000 expense.
William