Just a suggestion, but a year is a long time for storage. Suggest you find a relative or friend that would be willing to start your Prius every couple of weeks, and perhaps drive it to the store and back, to keep the batteries charged.
You could remove the 12-volt battery and connect it to a "battery minder" type trickle charger. Although, if your battery is more than a couple of years old, you might want to consider just buying a new 12-volt battery when you return.
If you have an Optima or similar AGM battery, it will hold a charge for a year or more. However, you need to disconnect it from your Prius by removing one of the battery cables; because there are parasitic electronics that are always on that will drain the battery in a month or so.
Not sure how long the traction (high-voltage) battery will hold a charge. Perhaps, others with more experience can advise; or you can contact the Toyota dealer for their advice. We have left our 2002 Prius parked for as long as 3 months, and the traction battery retained the charge. Not sure about a year, though.
Again, the best thing would be to have someone periodically start and drive your car in your absence.
It's really hard to let a car sit; they just rot into the ground. We had an old van that I parked for a couple of years after I was laid-off. When I was ready to start using it again, it was junk. Sold it for a little above scrap value to a teenage who was willing to keep repairing things until it would run reliably again. Took a big loss on it; a real waste of money.
Kind of extreme, but you might also think about selling it. Then, buy a newer, used Prius for about the same money, when you return.
Last edited by Phoenix; 06-04-2014 at 02:06 PM.