Battery heater question, what does "plugged in" mean?

You can toggle the traction battery heater on, in the Toyota software menu. I believe the factory default is toggled off. Ditto with traction battery cooling. There's also the question, is the heating pad installed by default or if it's a winter package option.
I do know that charge current is slowly ramped up, until battery reaches optimal temperatures, before full charging current is applied. The software's way of not destroying your battery.

 

I always thought the heater ran off the wall charge, are you sure it’s 12 volts?

I figured that’s why it had to be plugged in.
To run off of the 12 volt, wouldn’t it have to put itself in ready so the hybrid battery can keep the 12 volt charged?
And wouldn’t the engine have to run if the hybrid battery was low?

 

Those stupid Prius engineers think of everything!!! If it is indeed a 12V warmer; I'm pretty sure it's tied into the other side of the starter relay. ie. no ready mode no heater. If not, there would be many dead Prius out there in the winter time.
Get a jump box and give her a shot - report back your findings.

PS. I've plugged in many 110VAC heaters into 220VAC in an emergency. The carbon pile will run hot and eventually burn-up - hopefully we can accomplish whatever we need to do before that happens... I stand there the entire time, to literally put out fires....

 

No, power to close the charging relay - so no activation of the battery warmer, is my guess. If there's wall power, all bets are off...

 

Yep , when you plug your car in , you charge not only your traction battery , but your 12V battery as well is correct ..I may add that when battery heater is activated in the menu and the car has been fully charged and the car is left plugged in ; if the temperature of the traction battery drops near freezing , the brick will turn on to activate the the 14v output of the onboard charger to supply 12v for the heater and also keep the 12 battery happy.
I have notice that 6 hours after a full charge at -25C , the brick turned on and could hear a slight buzzing sound (inverter) under the hood (gen 4 prime has its battery under the hood) so power demand(200W) from the heater was provided by the plug and the 12 volt battery maintained charged by the charger

 

That's nice to know. I'll keep the car plugged in if the temperature is going to be below freezing (so for the next two months and a half here). Even if it's 24 hours a day with no car usage (unlikely), that will just add $15 a month to my bill.

 

Yes , there are two circuits for the battery heater for a total of 200 watts . It is not clear when the 2 circuits are activated simultanously , could be one and if it's not enough ,the second kicks in .BTW when the battery is warmed up, the heater turns off and monitors the temp ..ready to trigger it back on if needed.Last winter we had a polar snap for 48 hours with -25C average ....stayed inside, on the third day started the car . Outside temp was back in the -8 C , the car operated in EV .
PS battery warming for canadian models and Alaska can be operated for 30 days in a row.I do keep the car plugged in for January and Feburary with the heater function ON. Otherwise in above freezing temperature ,I unplug the car after charging.

 

Note that the Canada/Alaska/Greenland 30-day heating isn't a model difference - it's a scantool setting. Setting it on in relevant areas is part of the pre-delivery inspection, but it could be switched on or off later, even though it's not shown as a "customisation" in the user manual.

It appears that there are separate "reasonable operating temperature for 3 days" and "the car will start for 30 days" algorithms, with different thermostatic controls.

And the 30-day one operates independently of the charging schedule and "battery heater" control - those can normally be set to avoid drawing power, but if the "Canada" mode is enabled, it could draw power whenever it thinks it needs to protect the battery.