I spent a few hours of my Sunday afternoon changing out the battery on our Prius. Just like a conventional car, the Prius has a regular 12v battery. But instead of being located under the hood, the Prius auxiliary battery is located in the trunk, near the right rear tail light. Changing it is pretty easy. It just takes some time though because you have to remove a bunch of hardware to get at the battery. Not difficult, but just takes time. Also, the battery that fits in the Prius is costly; about $200! But it doesn’t bother me too much. The original lasted close to 7 years, which is amazing in Texas.
So far (7 years in) the Prius has been great. Averaging 46 mpg is pretty awesome! I just wish they made a hybrid mini-van as well!
If you are interested, the following video explains exactly how to change the battery. I had my phone propped up in the back of the car and just followed the steps. Easy peasy!