How Long To Flatten Aux. Battery? (without Trying)

[PhilA]

Hi all

What's the view of the assembled expert company on how long a Prius can be left in parked/alarmed state before the aux Battery goes flat? I got back from a 4 day trip to find one dead Prius in an airport carpark. Had to call out the RAC man with the Battery - annoyingly (but with some relief) I hadn't left lights on, internal or external. No drain apart from the standby systems and the alarm (which the carpark guys swore hadn't been going off all the time). The Battery charged up, I got home, with a 20k service due this last week.

So I ask the guys to check the aux battery health when I book the service. The message didn't get through, and all I get is a report of the charge state. But the other branch (it's Platinum in Bath - be warned!!) has the battery test kit. So I go there today and wait another 30 minutes. Result - inconclusive. They don't comment on battery health, but do say it's in need of a recharge. (This after a 30 mile drive). I ask a bit more, the service rep tells me that it's normal for the battery to go down in 5 days and it doesn't charge unless the petrol engine is running, which turns the alternator.

Quite. So I politely ask her if I can, as the notice says, 'talk to a technician'. Service Centre manager appears. He tells me that, though a battery isn't really flat (ie there's volts on the terminals) it won't necessarily be able to turn the starter motor. I remind him it's a Prius, ask him if the alternator might be to blame, because the petrol engine isn't running. He agrees. OK, I ask for the test results and think I'd better find another service centre.

So, given that I am not exactly impressed by their technical know-how, should I take the '5-day' advice with a pinch of salt too? Or should I be pushing for a replacement battery?

The test results BTW show a CCA of 229Amps, a condition of 'Good-Recharge', and a code of 2VNLH-CWJLB which is less than helpful too.

Despite all this, I still think it's a great car - the aux battery is the Achilles Heel, but maybe the technology is too advanced for the service centres. (or the training too retarded). I think my blood pressure is returning to normal now, it's the strain of staying polite when being told a load of old cobblers that I find difficult.

[OOTF]

I'm not an expert on these matters but I am an electronics engineer. If the aux Battery is not the main Battery but the one which starts the petrol engine and runs the general electrics of the car, I would expect it to last for weeks if not months and still be able to start the car.

If the alternator was not charging the Battery correctly, then the battery could have been low when you left it, in which case it could have been flattened by the relatively low drain over a short period of time.

One other thing, lead acid batteries do not recover from being left flat (0V) for several days. If the battery has recovered, there is a good chance that the capacity is severely reduced.

I would suggest that you get the alternator checked, to make sure it is charging the battery correctly and also get the battery checked before it lets you down again.

[Chris Dance]

You do not mention how old the Battery was. I have had a complete Battery failure on other cars after 2 years. (Not with a Prius as mine is not that old yet.) When you leave the prius the batteries energy is being used by the anti theft devices. With a fully newish charged Battery it should not go flat in 4 days. My son has left his Prius for 3-4 weeks without problems. I would suggest you change the battery from what you say it is not reliable now. I strongly recommend that only Toyota dealers service or repair a Prius.

Hope this helps. Chris.

[PhilA]

You do not mention how old the battery was. I have had a complete battery failure on other cars after 2 years. (Not with a Prius as mine is not that old yet.) When you leave the prius the batteries energy is being used by the anti theft devices. With a fully newish charged battery it should not go flat in 4 days. My son has left his Prius for 3-4 weeks without problems. I would suggest you change the battery from what you say it is not reliable now. I strongly recommend that only Toyota dealers service or repair a Prius.

Hope this helps. Chris.

Thanks for the reply Chris. It's 2 years old, original as supplied with the car. As I understand things, it's both the anti-theft devices and standby supplies for the various systems left sleeping under the bonnet. Most nights, the car lives in our garage so it's not locked - and for many of the days it's only doing short trips around town. We have LOTS of steep hills around here - problem being that we live on top of one, so the days end with a discharge probably! Quite agree with your recommendation about Toyota dealers - but that's my problem, the 'advice' I got is from Platinum Toyota here in Bath. It looks as though not all dealers are as conversant with hybrid systems as we want them to be. It's a part under warranty too, so there's a bit of reluctance on their part to admit liability I fear.

But you've convinced me there's a problem for them to sort - so I'm complaining at a higher level.

To OOTF:

Thanks for taking the trouble to reply. Maybe I didn't explain things clearly enough for non-Prius owners - there's no alternator as such on the Prius, nor a starter motor. The auxiliary Battery is a tiny (think motorcycle) lead acid Battery there primarily to power up the electronics, and the circuit isolators to the main power units, which are a humungous gorilla of NiMH (I think, not Lithium?) batteries, some 400+ volts. The electric motor which turns the wheels (in conjunction with the ICE) also acts as a generator, re-charging the main power cells. They in turn drive an (or probably several!) inverter which provides the supply for the circuits as well as charging up the aux Battery. But the big batteries are isolated once the system is off, ie parked/alarmed. So the annoyance is that this tiny squirt of a lead acid battery stops the whole thing from working. And because it's also powering the alarms and locks, you can't even get into the car without a great deal of palaver.

I just wonder if this is, in part, the reason that Toyota are fitting photo-voltaic cells on the roofs of the new model, not just to power the aircon, but to top up this battery and hide their shame?

[Teknys]

I just wonder if this is, in part, the reason that Toyota are fitting photo-voltaic cells on the roofs of the new model, not just to power the aircon, but to top up this Battery and hide their shame?

1st Aux Battery is probably at fault and not taking a full charge which shortens the stanby time considerably.

2nd New Prius with photo-voltaic cells on the roofs, this is for top grade models only and is designed to power extractor fans to maintain air flow through the car in hot climates so when you return to the car the interior is not so hot.

[Chris Dance]

I do think the dealer should change the aux Battery. The only other thing that comes to mind is a short but I think you can rule that out as your Prius was OK after the RAC chap got you going. I think the dealer is talking rubbish about recharge in 30 miles. I have no idea why they would say that if the Battery was OK. I think they must know the Battery is on its way out. Sorry to hear about your dealer if you are not satisfied with the service ring Toyota Customer Care.

Let us know the outcome please.

Chris.

[timberwolf]

What type of long stay car park was it? Did you have to leave the keys with the car park staff? Any chance that they tried to move the car and couldn't figure how to switch your Prius on and off correctly?

Was the 12v Battery removed from the car, and recharged on an intelligent Battery charger?

From what I've read, failure after 2 years is a bit early, failures usually seem to happen after 3 or 4 years. As Chris says, a new 12v Battery should easily last for 3-4 weeks, if the owner hasn't previously accidently drained or partial drained the battery.

Always lock the car, if a door or the hatch isn't shut properly then you should get a warning and the car will not lock.

I like your theory about living on top of a hill affecting your 12v battery charging :D

The Prius keeps the HV battery charged between 40% and 80% State of Charge (SOC), and if it has enough charge to spin the ICE by running MG1 (Motor/Generator1), then I would assume it has enough power for all the 12v systems as well. The 201v DC from the HV battery is converted for use by the various 12v systems via the DC-DC converter. The Aux 12v battery is charged when the Prius is in Ready, with a constant 13.8-14.1v, which is apparently not a good method of charging a lead-acid or AGM battery. From what I can understand, this means that the Prius 12v battery is never fully charged, I would guess about 75-80% charge, and apparenlty this type of charging results in a shorter life-span for the battery, hence the typical 3-4 years that is frequently mentioned in forums from owners that have had problems (I don't know if this is typical for all Prius owners though).

Your annual mileage doesn't sound too bad at 10k.

[Chris Dance]

Just by the side of the 12 volt Battery is another small electrical box. What is it and what is its purpose. Help please.

Phil A. I think you have a Battery that is not holding its charge.

[timberwolf]

Just by the side of the 12 volt battery is another small electrical box. What is it and what is its purpose.

Backup power for the brakes, capacitors are charged up to provide a backup I think to enable the driver to stop the vehicle should the 12v system fail.

[Chris Dance]

Thanks Timberwolf. We learn all the time.

I was asked today do have to plug your Prius into the mains every night. Just shows not too many folk know how good the prius is and what it is capable of.

[Mkuk0]

Just come back from a week away meself, car left in Airport car park, started no problem, I would seek another Toyota dealer and get a new Battery. My gripe is some bugger swiped my car and scuffed up front bumper..NOT happy!

[timberwolf]

That happen to my previous car (a Honda Civic), scuffed a thumb sized area of the painted bumper right down to the black plastic underneath, I'd only picked up the car a few weeks before my holiday, and it was parked at home.

[PhilA]

Thanks to everyone who's brought their comments to this. I go with the majority opinion, which is that I've probably got a faulty aux Battery but the struggle at the moment is to convince my garage / service centre this is so. It's a marginal call - I reckon the aux Battery has never been that well charged up, because of the way we use the Prius, which tends to be lots of short trips plus one or two 30-50 mile runs a month, with occasional 200+ miles. So I'm thinking that 1) the Battery was not too well charged anyway and 2) it's losing the ability to hold its charge. But the service centre 'test' says it's OK (I -hope- this is a proper discharge test, but even then they only test the cranking current amperage, not the long-term health).

The main worry is that such batteries, particularly puny lead-acid ones like this, don't take kindly to being flattened, so it's had a bad experience already.

In response to other questions:

there wasn't evidence that they'd tried to move the car in the carpark. Although it is a valet-parking site, I'd been told at the outset we wouldn't be moved on this time, and it's been left undisturbed on previous occasions. Windows were shut, and lights were off (including boot internals) - and it's not the sort of airport carpark where low-flying planes set off the alarms frequently.

The RAC guy (who was a Prius specialist and was, he said, well familiar to climbing into the boot to open the door because of flattened aux batteries) couldn't see any current leaks when we recharged, and according to his meter, the battery was taking charge at a good rate (an extremely frightening 100+ amps he said!) from the inverter supply.

In the last couple of weeks I've been testing where I can - both the onboard diagnostic and a voltmeter at the charging terminal under the bonnet. I'm never seeing a voltage (even after a 30 mile trip) more than 12.5 - which will drop to 12.3 with lights full on. I don't see much change, say 0.2 volt max, after 24 hrs locked/alarmed. The (lead) acid test comes later this month, with another stay at an airport. This time I hope to be better prepared, I'm putting my own reserve cold-starter battery in the boot, so if necessary, once I've climbed in, I can get myself underway. Hope I don't have to, though.

I suspect I'll be pushing for a replacement, or at least a long-term test in the service centre, when I can spare the time, I'll let you all know how we get on. In the meantime Customer Services have a 2 page letter from me, to which I await a reply....not so much about the state of the battery, but the misleading information I've been fed from the local 'expert' centre.

[Chris Dance]

I hope you get it sorted.

I am dreading getting a flat Battery, I thought you could only get a prius started by using the terminals in the front engine compartment? I also thought you could not unlock the car with a flat Battery with key fob. The key has to be used and then of course the alarm goes off.

How did your RAC chap get into the car if your anti theft devices were on?

It would be good to know the correct procedure if any of us get the flat Battery problem.

[PhilA]

I hope you get it sorted.

I am dreading getting a flat battery, I thought you could only get a prius started by using the terminals in the front engine compartment? I also thought you could not unlock the car with a flat battery with key fob. The key has to be used and then of course the alarm goes off.

How did your RAC chap get into the car if your anti theft devices were on?

It would be good to know the correct procedure if any of us get the flat battery problem.

The aux Battery was so flat the doors didn't open (nor would the alarm work of course). So I used the mechanical key (inside the fob) to open the driver's door - then opened the bonnet. Then used the charging terminals under the bonnet (inside the fuse box - it's shown in the car manual) to give a first charge to the aux Battery. That meant the alarm went off - so ideally your partner is there to disarm it with the remote! Then we could open the boot, expose the aux Battery, which the RAC man said he prefers to charge directly at the terminals, rather than through the bonnet terminal. In theory we could have started the system up straight away, but he wanted to do a couple of checks first, and give an initial charge. All was OK, so then we turned the main systems on (which was possible without the temp battery connected) - that meant the main battery/inverter system started charging up the aux battery, and in turn the petrol engine started up. For safety, and while he did the paperwork, we left it 5 mins before driving off, but if all was OK then in theory you're good to go as soon as the system is powered up, provided the ICE starts.

If we hadn't been able to open the boot (ie both the aux battery and the keyfob battery were down, and for some reason the switch wouldn't work) then there is a mechanical way to open the back door, as shown in the manual. But that involves crawling into the boot from the passenger compartment.

[timberwolf]

The RAC guy (who was a Prius specialist and was, he said, well familiar to climbing into the boot to open the door because of flattened aux batteries) couldn't see any current leaks when we recharged, and according to his meter, the battery was taking charge at a good rate (an extremely frightening 100+ amps he said!) from the inverter supply.

Thanks for the update.

[GreenJuice]

I go with the majority opinion, which is that I've probably got a faulty aux battery but the struggle at the moment is to convince my garage / service centre this is so.

In the last couple of weeks I've been testing where I can - both the onboard diagnostic and a voltmeter at the charging terminal under the bonnet. I'm never seeing a voltage (even after a 30 mile trip) more than 12.5 - which will drop to 12.3 with lights full on.

You may have already done it this way, but I thought its worth posting in case others might like to found out how to access the "Maintenence screen" on the MFD. If the car's own screen shows a failing Battery, you shouldn't have much of a problem convincing the garage! The method is detailed here.

I found a useful post suggesting that your basline voltage should be 12.6 - 12.8 V when fully charged. You might other useful posts on that website, but it sounds to me like you may already have enough evidence of a failing Battery.

Incidentally, I have previously left mine at an airport carpark - 15 days, no problem.

Thanks for posting your "how-to-get-out-of-jail" technique!

[Chris Dance]

PhilA and Greenjuice. Thanks for the information. I have printed it off. let us know what happens in the future.

Regards Chris.

[gniie]

At this stage there is enough input from the club members to give an idea that you may have a faulty Battery.

My experience also supports that theory.

I imported a Prius from Japan and all the evidence suggested that the car wasn't used for long periods at the time. When the car was back on the road I've experience similar symptoms wrt the aux Battery. Multiple short trips combined with the occasional long trips were not enough to keep my aux Battery fully charged and the use of any energy consumer(radio, lights, emergency lights) without running the engine(=ready mode) would drain the battery v quick. I had to replace it eventually and I had no problems since.

My conclusion was that if the car is not used regularly and is few years old, the aux battery looses the capacity to fully recharge and discharges way to quick.

Another point that I want to make to anyone that does have to recharge the aux battery on a Prius: I was recommended by my v helpful Toyota mechanics that the battery should be trickle charge and never fast charged as it will further damage the batteries capacity.

Good luck with your problem

[Joncon]

PhilA

What cold-starter Battery do you use?