Hybrid Car – More Fun with Less Gas

Dead Battery - Page 4

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Posted by Mr. G on February 27, 2008, 11:18 pm
(Chas.Gill@gollum.btinternet.com) says...

When the Prius is off, the HV battery is physically disconnected from
the electrical system via a solenoid. (you can hear it "click" from the
back of the car when you are starting it.)

The solenoid will engage when the car is in the 'On' or 'Ready' mode; in
the 'Acc' mode (1 push of power without brake), it is still
disconnected, so the electrical power is only coming from the 12V

Posted by TKM on February 28, 2008, 1:38 am

 It would indeed be useful to know which battery powers what.  Certainly the
Prius 12 volt battery is physically smaller than the battery in many other

What I recall doing before leaving the car off for a week was driving
several short trips at night in rain and snow with the wipers, electric
defroster, lights and heater motor all on.  To me that's heavy accessory use
since the battery probably doesn't get fully charged.  Cold weather also
reduces battery capacity.   I very seldom use accessory mode and haven't for
some months. But, lesson learned.  The Smart Key System gets switched off if
the car is to be left off more than a couple of days especially in the


Posted by Elmo P. Shagnasty on February 28, 2008, 2:00 am

So turn the Prius on in accessory mode and find out.

Posted by Mr. G on February 28, 2008, 11:57 pm
 Shagnasty (elmop@nastydesigns.com) says...

When the HV battery is engaged, there is an inverter which, among other
things, supplies power from the HV battery to the 12V bus.  The only
need for the 12V battery is to supply power to the electronics when
first starting the car, and also for power in the ACC mode, which as
previously pointed out, is not a good thing to do for any extended
period of time.

Posted by TKM on February 29, 2008, 6:09 pm

Thanks.  That's very good information.  Rather than jump start the Prius
next time the battery is down, maybe one of those battery packs that plugs
into the dashboard power outlet would do the job.  It certainly doesn't
sound like much power would be required.

I"m also looking for a Prius wiring diagram.  That ought to be good for a
few days of reading.


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