mothballing

An older High Voltage battery sitting around isn't generally a good thing, but I'm not so sure there is much you can do about it. Any chance you can have a friend / relative stop by once every other week and take it for a spin for a few good miles? On a sidenote, if that High Voltage battery is still under your manufacturers warranty then you have no worries - other than the 12v that is.

 

Same thing. But a smart tender type charger........NOT a cheap trickle charger.

 

No

 

Best thing you can do is run it in place. Even a few minutes a month would help. A 12v battery tender & some gas stabilizer wouldn't hurt, but just running the sucker should be tool #1.

 

Does the Prius c have a way of disabling SKS? Doing that would stop the car continuously looking for a fob. I believe some older Prii had a switch to do that. You may find a menu option.

 

I thought you had been around enough to NOT say that. But I guess not.
One should NOT run a gas engine "a few minutes a month", thinking you are somehow doing a good thing.
It is NOT a good thing.
When the engine is cold, condensation forms in the exhaust and gets into the pipes and muffler and into the crankcase.
It is not good to have a shot of water put into an engine every month or so.

IF.....you think you MUST start it periodically, it should be run as continuously as possible for about 30 minutes or until you are sure it is completely up to FULL operating temperature. The best way to do that is to drive it.........around in a big circle.
Driving is not the problem; stopping where there are people IS.