The HV battery should still be under the original hybrid warranty: 8 yrs/100,000 miles. Check the original purchase date to see exactly how much time you have.
It looks the original purchase date was October of 2008, meaning I should have the warranty until October of 2016. I'm assuming it wouldn't be a bad idea to know the state of my battery, though, even if it is under warranty? Also, would having it assessed at regular intervals be a good idea?
What would you do with the information? If it's just for the thrill of gettting anxious, go for it! Seriously though, before taking additional steps it seems as if you ought to reason out what good will come of it.
First, read up on any random thought concerning Prius care that comes to mind. Even the seemingly benign. "How do I change fog lights?" or "How do I check turbidity?" Read up especially on keeping filters clear/clean. Second, I highly recommend an independent Hybrid shop in your area. If you can't find one, ask the dealer if they can perform an HV battery assessment. Get the print-out. First find out if they will give you a print-out. If they can't do an assessment see if you can learn how. Read up on grid-chargers. I like what I've read, but I don't have an outlet in my garage. It may not be for everyone Third, get a scan tool. Several posters here have recommendations and can tell you why. Enjoy!