12V Battery Dead From Heater Use

I'm puzzled. Does this mean that if the engine never runs, the only charge the 12-volt battery gets is a maintenance trickle charge? And, if it runs the climate system during pre-conditioning and then one only drives in EV mode, how does the 12-volt battery get back to full charge?

If the car spends only enough time connected to its EVSE to recharge the traction battery -- about two and a quarter hours -- and that is the only trickle charge the 12-volt battery gets, then how can one make reasonable use of pre-conditioning without depleting the 12-volt battery? Is there something akin to a conventional alternator which charges the 12-volt battery when the car is moving, regardless of whether the motive force is from the electric motor or ICE?

Based upon your comment, it sounds like pre-conditioning initiated by the the Entune app or by the key fob is not the same as turning the car on and leaving it in "park" with the A/C running. That's not surprising because the remote pre-conditioning runs only for a brief time period of ten to fifteen minutes, while turning on the A/C manually just turns it on. Even so, how does the 12-volt battery get back to full charge in either situation?

I'm still trying to understand this technology. Any comment by the Prius Prime tech gurus would be appreciated.

 

I had always thought the AC system ran off if the HV battery.

 

Welcome to the forum. Would you please disclose where you found this information since this could potentially be a pretty big deal to all of us.

 

welcome!
hvac is 220 volts or so, and runs off the hybrid battery. i'm not sure how the prime handles the situation you describe. as you say, if it weren't plugged in, it would go to ready and run the engine to recharge the hybrid battery.
it wasn't the hvac that ran down the 12v, but perhaps some other accessories. i think you need to review your procedure again, i wouldn't think you could even run the hvac while plugged in, except remotely.
has anyone else tried this? i know the pip won't allow it.

 

A rule of thumb for all Prius vehicles is that the accessory mode should only be used for short durations i.e 5 minutes due to the small 12v battery.
The ready mode is a very efficient mode to leave the vehicle in for extended periods of time for climate and accessory use. I often leave my Prius vehicles in the ready mode for hours at a time at the drive in theater.

 

Exactly what I wanted to say.

The battery drain he experienced might just be as a result of not readying the car. That's just what happened

 

can the heat run on a prime when not in ready?

 

What is a drive in theater?

 

Just in case you are serious.

Drive-in theater - Wikipedia

 

Pregnancy avoidance test facility.

 

The old big screen CRT TV in the back of the man cave garage. You can even use the climate prep while "Plugged-In". "Pregnancy avoidance test facility" Yep it's not happening in the back seat of a Prime. Bet you got a "Charge " out of this.

Waiting for someone to test all the things that will run off the 12v system in accessory mode. AC/Heatpump? Really? Ican see maybe the blower..

 

What is accessory mode and ready mode? This happened to me today. Since I have a Premium not an Advanced, I have no option to warm up the vehicle from an app. So I kept the car plugged in, and attempted to turn it on and it came up to the display screen, so I turned on the heat as well as the seats. Came back out less than 15 mins later and car had just died and kept it plugged in but it's still dead. Luckily I noticed that the heated seats lights were on at that point and turned those off. But why was the car dead, yet the heated seats were still showing as powered on???!!!! I don't know if plugging it in is going to do anything as there is no green light on and I could not get it to start to see if I had to switch it over to "charge now" vs in the morning which is what it seems to like to default to....

 

In accessory mode, the car is only getting power from the small 12 volt accessory battery. In ready mode, the car is getting power from the big traction battery. So, don't run the car in accessory mode, which in a Prime means unplug the charging cable before turning the car on.

 

maybe there is enough charge left in the battery to run the switch leds. kinda surprised it lets you run the seats off the 12v in acc mode though. i would check the 12v voltage.

there is no option to warm up the vehicle on any trim. if you want to pre warm the cabin or engine, unplug, foot on brake, press power button once. set hvac to desired output. for engine warm up, press hv button or front defrost

 

Ok, ty for the details that I needed to understand the process! Although I came out one morning and the back window had heavy due set on the car overnight and it seemed like the rear defroster had been on as the window was defrosted in the pattern that occurs when the rear defroster is on.... I had not been outside to warm it up but it had been plugged in overnight.... if it was set to charge for morning departure, would it somehow have also warmed the cabin to a point of defrosting the rear window?

 

Update: The Prime's regular battery had to be jump started and then plugged in to charge. As I was at work and my husband jump started it during the day, I'm not sure if the traction battery was dead too or what. (And my husband knows even less about how to work this car than I do....)

 

if the regular battery (12 volt under the hood) was dead, you left something on by mistake.
you should really buy a battery charger and charge it up for full health.

you cannot drain the traction battery below allowable levels, that is not a concern.

 

For a more detailed explanation of the relationship between the 12-volt system and the 600-volt traction battery system, take a look at this 40-minute video about the Prime's "inverter/converter" from John Kelly at Weber State University:

As I understand it, the relevant take-aways are

• the 12-volt DC systems in the Prime (headlights, radio, window motors, etc.) are similar to most vehicles
• the computer, sensors and related control systems are also 12-volt DC systems
• the 12-volt battery powers these systems when the Prime is not in "ready" mode
  
• the "traction battery" provides 350 volts DC
• when the Prime is in 'ready' mode, the inverter/converter takes 350 volts DC from the traction battery and 'converts' it to 12-volts DC to charge the 12-volt battery and to run the various 12-volt systems
  
• when the Prime is in 'ready' mode, the inverter part of the inverter/converter, takes 350 volt DC and 'inverts' to 3-phase AC to power the motor which propels the vehicle
• the inverter/converter also provides power to the heat pump for cabin heating and air-conditioning

Possibly those more knowledgeable than I can offer additions and corrections to the above.

 

It wasn't by mistake... I thought I could keep it plugged in + warm it up... apparently it must have been in accessory vs ready mode though I am assuming in hindsight....