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Sagitar

The Curse Of The 12V Battery Strikes Again

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I have been driving my current Prius (no pun intended) since last September without any problems.

Last Tuesday, at about 1 p.m. I tucked it away in its nice warm garage and went away for a couple of days.

On Saturday morning I opened the garage with the intention of getting out the car and performing its weekly check of fluids, tyre pressures etc., but it would not start. This was not a question of the Battery being low, so much as absolutely flat. Not a peep. No indications at all when I pressed the power button, no courtesy lights, no security indicator on the dash, nothing.

The car doors were not locked so I had no difficulty getting into the car and popping the bonnet, but the boot lid would not open. I used my "booster" Battery on the post in the engine compartment to start the car, drove it a couple of miles, then put on the trickle charger.

I used the car without difficulty on Saturday afternoon, then left the trickle charger on until Sunday morning when the Battery appeared to be fully charged.

I have no idea what flattened the Battery. Nothing was left on as far as I know. All the doors were properly closed; no lights - internal or external - were switched on; the car was not locked so there should have been no alarm or key activity.

It will be interesting to see if and when it happens again.

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Sorry to hear about that Sagitar. Off the top of my head I cannot think of anything obvious . My only thought is that although your car is new, the Battery may not or have suffered one or two deep discharge cycles before you got it and is now a bit iffy.

You could try checking the voltages of your 12v Battery and see what you get as below:

  • Voltage across 12V Battery when car is IG-OFF (all doors closed and locked, Smart fob far away [more than 15 feet.] - if applicable) and has rested overnight (this will show approximate state-of-charge, 12.9V represents 100% charge of AGM Battery, 11.9V represents approx. 0% charge.)
  • Voltage across 12V Battery when car is IG-ON and headlights on (the difference between the voltage measurements at 1 and 2 is is an indicator of the Battery's capacity, the bigger the difference the weaker the Battery is becoming)
  • Voltage across 12V Battery when car is READY (this will give an indication of how well the DC/DC converter is maintaining voltage on the 12V bus, and therefore, applying charge to the 12V Battery)

To get into IG-OFF mode do not press any buttons.

To get into IG-ON mode press the START button and then press a second time both with your foot OFF the brake.

To get into READY mode press the START button once with your foot ON the brake.

If you can find the time to take those readings and post them it will give an idea if your 12v is in a good state.

HTH.

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could connecting the mains lead have charged the 12V, or does it need some current to be able to do that?

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Have Toyota Europe (those responsible for the Auris HSD 'issues') redesigned the electrics on the latest model European Prius too?

I hope not, but the legendary Japanese reliability of Toyota does seem to take a hit whenever the Frech 'designers' have a pop at it.

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Sorry to hear about that Sagitar. Off the top of my head I cannot think of anything obvious . My only thought is that although your car is new, the battery may not or have suffered one or two deep discharge cycles before you got it and is now a bit iffy.

You could try checking the voltages of your 12v battery and see what you get as below:

  • Voltage across 12V battery when car is IG-OFF (all doors closed and locked, Smart fob far away [more than 15 feet.] - if applicable) and has rested overnight (this will show approximate state-of-charge, 12.9V represents 100% charge of AGM battery, 11.9V represents approx. 0% charge.)
  • Voltage across 12V battery when car is IG-ON and headlights on (the difference between the voltage measurements at 1 and 2 is is an indicator of the battery's capacity, the bigger the difference the weaker the battery is becoming)
  • Voltage across 12V battery when car is READY (this will give an indication of how well the DC/DC converter is maintaining voltage on the 12V bus, and therefore, applying charge to the 12V battery)

To get into IG-OFF mode do not press any buttons.

To get into IG-ON mode press the START button and then press a second time both with your foot OFF the brake.

To get into READY mode press the START button once with your foot ON the brake.

If you can find the time to take those readings and post them it will give an idea if your 12v is in a good state.

HTH.

Thanks Joseph - This morning I ran the check that you defined, with the following results:

State (1) - 12.6 V

State (2) - 11.9 V

State (3) - 14.9 v

could connecting the mains lead have charged the 12V, or does it need some current to be able to do that?

Thanks Pete. I had charged the traction Battery before putting the car away, so I know it was fully charged, but my understanding is that it transfers energy to the 12V Battery only when the hybrid system is "on". It's irksome to think that there is about 3.5 Kwh of energy stored in the car and I cannot use any of it to boot the system, but I guess there are good technical reasons for not allowing transfer when the system is "off".

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Sorry to hear about that Sagitar. Off the top of my head I cannot think of anything obvious . My only thought is that although your car is new, the battery may not or have suffered one or two deep discharge cycles before you got it and is now a bit iffy.

You could try checking the voltages of your 12v battery and see what you get as below:

  • Voltage across 12V battery when car is IG-OFF (all doors closed and locked, Smart fob far away [more than 15 feet.] - if applicable) and has rested overnight (this will show approximate state-of-charge, 12.9V represents 100% charge of AGM battery, 11.9V represents approx. 0% charge.)
  • Voltage across 12V battery when car is IG-ON and headlights on (the difference between the voltage measurements at 1 and 2 is is an indicator of the battery's capacity, the bigger the difference the weaker the battery is becoming)
  • Voltage across 12V battery when car is READY (this will give an indication of how well the DC/DC converter is maintaining voltage on the 12V bus, and therefore, applying charge to the 12V battery)

To get into IG-OFF mode do not press any buttons.

To get into IG-ON mode press the START button and then press a second time both with your foot OFF the brake.

To get into READY mode press the START button once with your foot ON the brake.

If you can find the time to take those readings and post them it will give an idea if your 12v is in a good state.

HTH.

Thanks Joseph - This morning I ran the check that you defined, with the following results:

State (1) - 12.6 V

State (2) - 11.9 V

State (3) - 14.9 v

could connecting the mains lead have charged the 12V, or does it need some current to be able to do that?

Thanks Pete. I had charged the traction Battery before putting the car away, so I know it was fully charged, but my understanding is that it transfers energy to the 12V Battery only when the hybrid system is "on". It's irksome to think that there is about 3.5 Kwh of energy stored in the car and I cannot use any of it to boot the system, but I guess there are good technical reasons for not allowing transfer when the system is "off".

Those results would indicate that your 12v Battery is not holding its charge and is in need of replacement. It would be interesting for your dealer to explain how it has arrived in this condition after only after a little over 5 months.

12.6v indicates approx 70% charge, and the fact it drops to 11.9v indicates that it is not holding its charge. The 3rd reading indicates the charging voltage is ok.

At least it should be replaced under warranty, providing you can get them to accept the Battery is defective.

I hope it goes well, and let us know how it turns out.

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Have Toyota Europe (those responsible for the Auris HSD 'issues') redesigned the electrics on the latest model European Prius too?

I hope not, but the legendary Japanese reliability of Toyota does seem to take a hit whenever the Frech 'designers' have a pop at it.

Hi Grumpy - how are you doing?

This is no change as far as I am concerned. I had a similar occurrence within a few months of getting the Prius T-Spirit that I owned before the PiP. I recall that you and I took delivery at about the same time. At that time I didn't have the kit to rescue myself and had to call out the RAC. I described the conversations that I had with the dealer, who claimed initially that the Battery tested OK but eventually admitted that there was a dodgy cell and changed the Battery under warranty. I had no further problems after the Battery was changed, but it shook my confidence in the 12V system and caused me to spend money on a sophisticated trickle charger and a boost Battery. Because I have these devices, the latest incident was no more than a minor nuisance, but I would rather that it did not happen.

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I think that my 12v is probably the only thing in my car that's been reliable :)

And I hope I don't tempt fate by saying so. Is there a bad batch of 12v's and I've just been lucky?

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Those results would indicate that your 12v Battery is not holding its charge and is in need of replacement. It would be interesting for your dealer to explain how it has arrived in this condition after only after a little over 5 months.

12.6v indicates approx 70% charge, and the fact it drops to 11.9v indicates that it is not holding its charge. The 3rd reading indicates the charging voltage is ok.

At least it should be replaced under warranty, providing you can get them to accept the Battery is defective.

I hope it goes well, and let us know how it turns out.

I connected my Optimate charger again and the diagnostic data showed no problems with the Battery so I doubt I'll get anywhere with the dealer on the basis of this one incident. I've noted it and reported it to see if they react, but I'll wait to see whether it happens again before I go further.

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I'd say that for it to be completely dead in a couple of days, there must have been a drain of some sort. I doubt that a Battery which is not holding a charge would end up completely flat in 3-4 days, it would most likely still have a little charge in it.

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I'd say that for it to be completely dead in a couple of days, there must have been a drain of some sort. I doubt that a battery which is not holding a charge would end up completely flat in 3-4 days, it would most likely still have a little charge in it.

That makes sense and I am sure it is what the dealer would be likely to say, even though I cannot identify any obvious source of a drain. Which is why I will wait for a repetition before I start jumping up and down . . . . :)

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