How long can it sit?

the hybrid battery is fine long term. it's the 12 volt you have to worry about. the best course is to research trickle chargers here and connect one while you're away. the problem is, there's no way to know how healthy the battery is. just because the car is new, doesn't mean the dealer didn't run it down a few times before you bought it. these tiny batteries don't take well to that sort of abuse. i have left mine for six weeks in unheated garage with no problem, but you have to ask yourself, 'do i feel lucky'?

 

For a week?

If your battery dies because your car sat in the garage for a week, you didn't cause a problem, you detected a problem!

The aux (12v) battery is obscenely weak in the Prius, but you should be fine in the garage for a few weeks at a stretch if you shut the car down properly and don't leave the key fob in or near the car.
If you're concerned about this, then look into replacing the OEM aux battery with an upgraded aftermarket (Optima) battery.

Then?
Don't worry about it any more.

 

If you're worried, get a "Battery Tender" or a "Battery Minder". They are designed to be connected to a 12V lead-acid battery for 6 months at a time, for use in things like ATVs and motorcycles. You can install the included "pigtail" so you just connect a connector or you can pop off the front fusebox cover, flip up the "boost point" plastic protector, and connect a clip lead to the boost point and chassis.

Pearl S is hibernating in the garage, with a "Battery Tender" connected to her. She has trouble getting over the 18" and larger snow windrows our wonderful city leaves everywhere. So I drive "Bruiser", an FJ Cruiser, in winter, trying to use up all that surplus gasoline we have.

 

My impression is Gen3 is much less 12v battery drain than Gen2 (older pre-2010 Gen2 we have a SKS switch under the steering wheel which should be turned off for sitting car long periods). So I am thinking a week or two is OK in Gen3 but some would opt to manage the 12v battery as a precaution.

 

I pretty regularly go 1-2 weeks with no issues, and occasionally longer (3+ weeks). I think my parents went about 7 weeks with no problem. If it dies in less than a month or so, there might be something wrong (weak 12V battery, a key stored near the car, etc.).

 

2011 Prius. I routinely leave my car parked for 3–4 weeks. Just left it for 4 weeks and it started up fine, even in 30ºF weather. I also have a Metromile receiver plugged into the OBD port, which I assume drains the battery further.

 

2011 Prius. I routinely leave my car parked for 3–4 weeks. Just left it for 4 weeks and it started up fine, even in 30ºF weather. I also have a Metromile receiver plugged into the OBD port, which I assume drains the battery further.

 

yes, you said that already.

 

Not sure just how long it can sit. I know this, I parked ours for 6 months. Expected it to be dead. Fired right up. Wife said she started it a few times during that period, but never drove it. And that is the truth. Look at my fuelly records, you will see a area during winter to summer of 2015 where no fuel was added. That is the time I am speaking of.

 

Just returned from a six-week absence and my 2017 Prius Prime is dead. Happened one other time, I forget how long it sat then. I have a trickle charger which I guess I will be using from now on.

 

Yeah there's two camps of opinion above. My take: if the car is not going to be driven that day, on goes the charger, in my case a CTEK 4.3. I installed a quick connect (came with the charger) to make it easier. Maybe overkill, but I don't care.

 

Connecting the EVSE for a long while after you got back didn't allow it to trickle charge back up to a usable level? Or will it not even accept a charge if the 12v is dead?