Dead Battery

After a week of sitting in the garage, we got into our 2006 Prius and found there was no power--everything was dark and dead. After finding and uncovering the 12 volt battery, I checked the voltage and found it to be 2.5 volts -- definitely discharged.

A jumper from another car got the Prius going; but I'm curious. Has anyone else had this experience? The car was turned off normally. No lights were left on and we we just do the usual city/country driving . The propulsion battery was fine and showed a normal charge as soon as the car started.

TKM

Reply to
TKM
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I had it happen once, when the car was about a year old or so. I don't know why it happened, either.

Reply to
Michelle Steiner

Just about everyone who didn't bother to read the owner's manual.

Your car has the Smart Key System (fortunately, my base model doesn't). It runs all the time, using up battery power. If you're going to let your car sit, the documentation specifies that you turn the SKS off.

Reply to
Elmo P. Shagnasty

Keep in mind that some systems such as the Smart Key system require power even when the car sits unused. This is why the owners manual recommends turning off the battery when you know you won't be using the car for a week or more. The switch is under the steering wheel near your left knee.

Reply to
Shawn Hirn

The above is true, but our 2004 has been left for a week without having a dead battery. However, there were two other times the battery really had been depleted, it turned out someone had been sitting in the car listening to the radio and then "thought" they turned it off. Either it was left in the accessory mode or in the "on" mode (but not started). We now double check that the car is really off if we have done something unusual like use the accessory mode in a parking lot. ...Pat

Reply to
greenpjs

I think it depends on the state of charge of the 12V battery to start with. I was hospitalized for 5 weeks (and unable to drive for another week) and had my family turn off the SmartKey system (thank Ghod one daughter is a computer nerd and able to figure out what I was asking for), and the family drove the car once in a while, so it didn't lose the 12V charge. It was a couple of more weeks of driving before I turned the SmartKey back on; during that time, I took the car in for a state inspection; it was interesting to watch the mechanic get in the car, and then try to figure out just why the damn car wouldn't just turn on when he pressed the button.

Reply to
Pete Granzeau

I have a 15V solar cell and added contacts that enable simple connection to the battery lines. Works fine...

Reply to
e

Something was left on. Of course now it's impossible to prove either either way.

Reply to
richard schumacher

That switch turns off the SKS. There is no switch which disconnects the

12V battery.
Reply to
richard schumacher

I have left my 2007 Prius at home and at long term parking lots for more than a week several times and had no problem starting it. I would imagine the smart key system draws only a trickle of power in the listening mode.

I think the recommendation should read "if you wont's be using your car for weekS (plural)" or maybe even months.

In this case it's more likely someone left radio on.

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Reply to
fuelzilla.com

Thanks for the useful comments. A recheck of everything (lights, radio, etc.) indicated that nothing was left on; so it was likely the Smart Key System plus a 12 volt battery that was not at full charge because of short trips or heavy accessory use just before the week-long shutdown. Very cold weather during that time may have contributed too.

What I plan to do (when the weather warms up!) is to check the current draw of the Smart Key System against the capacity of the battery to get some idea of what Toyota means when they say to turn off the Smart Key System when "the vehicle is left for a long time". I also think an indication of the state of the 12 volt battery would be a good addition to the display roster.

TKM

Reply to
TKM

Right, and the SKS continuously draws battery power so switching it off saves battery power.

Reply to
Shawn Hirn

Ah, now it comes out: "heavy accessory use" is the culprit here. The ACC position should not be used for more than a very few minutes at a time because it tends to kill the undersized 12V battery. Unless the car is in an enclosed space, when accessories are in use it should be left ON and in Park so that it can manage its own energy as it was designed to do.

Reply to
richard schumacher

If I recall correctly from a couple of years ago, one of the biggest power drains is the dashboard display. In fact I recall hearing (or reading) somewhere that it's best to avoid using it in the accessories mode for more than 30 minutes as it had a tendency to discharge the battery. As a matter of course, therefore, if I happen to be using the radio in accessory mode I always turn off the display via the menu, as a precaution. However, the dealer didn't say WHICH battery and I'm fairly sure I've read somewhere else since that the 12v unit is really only there to power low wattage critical systems (such as engine management and other systems at start-up) and that everything else is energised by the HV unit, so I'm not really sure whether what he said was true or not. Perhaps there is an expert reading this that can clear this up?

Reply to
Chas Gill

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 battery.

Reply to
Mr. G

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 cars.

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 winter.

TKM

Reply to
TKM

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

Reply to
Elmo P. Shagnasty

Once the car is in Ready mode, the 12V battery powers nothing. All the electric power comes from the traction battery and the motor/generator. So using your wipers, electric defroster, lights and heater motor while driving will have no impact on your 12V.

Reply to
Marilyn & Bob

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.

Reply to
Mr. G

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.

TKM

Reply to
TKM

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