How to take care of Prius when not in use?

there's no science. once a week should be fine if you can put a tender on the 12v.

 

I would take it for a good drive at least once weekly, say 10 kms minimum, use the AC a little, to circulate it's oil. The rest of the time let it sit in the garage, with the 12 volt battery hooked up to a smart charger (3~4 amp range), one that can be kept on indefinitely if needed.

 

I have been storing two Prius's for six months at a time for a number of years. I have the oil changed before putting the vehicles in storage and I make sure the drive battery is close to or fully charged. I leave a battery tender on the 12-volt battery. Neither vehicles are started during the 6-month storage periods. The only concern I have is that usually the engine knocks for a few moments when they first start up. I have talked to the dealer about the noise and they tell me if they don't hear it, they won't do anything about it.

 

I'd say the brief knocking is not a problem, just a result of all the oil on the components having had 6 months to run off and down into the oil pan. At that point they aren't well lubricated and will be noisy. As soon as oil is recirculated throughout the engine upon starting it, the noise should stop. Technically you're hearing engine wear, but it should be negligible over the life of the engine as long as you're not revving the engine while it's making noise.

 

I don't think a single day would count as having the car sit idle for too long. IMHO doing this daily or every other day does more bad than good. You are starting from cold every time with all the wear that is connected with it.
There is no need whatsoever to keep the hybrid battery charged like that. It should not discharge that much.
Maybe if you do it every month I could understand it.

 

Every month is too little. Once a week more likely.

 

I've had my car sit idle for 3 weeks during my holiday. No effect whatsoever.