Dead car -- is my diagnosis correct?

DrD,

Two questions:

When you say, "leaving the car 'On' all night," do you mean in the
"Ready" condition? (Ready light on dash is illuminated.)

After you jumped the battery, when you first started the car, can you
say how many bars showed on the SOC, and what color were they?

 

If you leave a Prius on in Ready while in park, the 12V battery will be charged as needed. I suspect you left a light on or a door open.

Tom

 

The pieces aren't adding up right here, something's missing.

As I understand it, if the car was in Ready, and running, even if the
12v battery was dead, there would still be 12v from the DC to DC
converter. And the ICE would cycle on all night as needed to keep the
HV battery at a low charge.

So no matter what the origin of the draw on the 12v system, the car
should have been running all night...

But, if you hit the Power button first thing in the morning, having
forgotten that the car was in ready, it would have shut everything
down. Now, if the 12v battery was shot, when you hit the Power
button again, nothing would happen.

Is this the missing piece of information?

 

DrD,

If the car is in Ready, yes by running the ICE to keep the HV battery
charged, the 12v bus will remain 'hot," providing power to all the 12v
electronics and keeping the 12v battery topped off.

Are you absolutely sure of this? If there were no dash lights or MFD,
then the car was not in Ready, or you had run out of gas during the
night. If it was not in Ready it was in either Off, On, or Accessory. To
be in either one of these, the night before you would have had to turn
the car first to Off, and then to one of the other two.

The simplest explanation that seems to fit -- Occam's razor --- is that in
a moment of abstraction, inattention, or preoccupation due to the
illness you did turn the car Off the night before, and the battery was
drawn down during the night.

Well, at this point the 12v battery was truly dead. The question
remains how did it get that way.

As it sounds like the trailer wiring harness has at least the negative
lead common with the battery, and not connected to the tail light
wiring, there may be some fault in the trailer wiring or hook-up such
that it is directly draining the 12v battery, or...

you turned the car to either Off or ON (one push of the Power button
with the brake pedal not depressed) the night before and, as was
suggested by qbee42, in a moment of distraction you left
an interior light on or left a door or the hatch ajar.

While you're thinking about these things, better check to be certain
that the 12v battery ground connection to the body is tight and secure.

 

DrD....its very simple. You left a door or the back hatch cracked and it killed the boot battery because you did not observe what almost every single person who comes on here and reports dead boot battery and that is you do not lock the door with either the fob or press the outside door button setting the alarm.

There's been a few "I left the car running all night" posts here lately too and thats why.

Which is no big deal as the car's engine will happily come on now and then regularly all damn night to keep everything charged and will contiunue to do so unitil it runs out of gas. Or it gets stolen.

If the car is READY and you get out and try to lock it , it will not allow a lock and beep one long beep and if front door cracked will do the same. Get in the habit of locking the car every single time even in the garage. FOB or door button.
I know you have the FOB on you.
Good Luck.

 

It's also the time to point out that once you've drained a 12V, it will never be the same again. It has lost a lot of capacity due to this event.

 

Yeah lead acid batteries don't like to be fully discharged, that's for sure. Recharging it promptly as the OP did can minimize the harm though. If you let a lead acid battery go completely flat and then leave it like that for a few months then it's often completely unserviceable.

 

Just for the sake of completeness, not that I'm suggesting it happened in this case, but it is possible to run down the battery with the Prius in Ready. If you leave the car in Neutral, it will not start the ICE and charge the HV battery. The HV battery will slowly draw down until it reaches a critical level, and then everything will shut off with an impressive display of warning lights. If a light is on, the 12V battery will then draw down because it is not being charged by the dc to dc converter. Note that the Prius warns you about this if you leave it in N.

Tom

 

A depleted battery will also freeze... breaking lots of the insides. Don't let a lead acid battery get very far down at all if you park in freezing temperatures.

 

I would agree, you probably did turn the car off, but something was still on, maybe a door ajar.

In that situation, whatever was on was running off of the 12v battery, draining it.

The SOC of the traction battery being up in the blue reinforces this, as well as the fact that it was not out of gas. With the 12v battery dead in the morning, when you tried to start the car, you would get nothing. The 12v battery starts up everything else and throws the relay to the traction battery. Without the 12v battery, the traction battery cannot be connected to the system - thus no power, no nothing.

 

Where were you when you powered off the car? Did you reach in from the passenger side?