Non-Technical Owner Requesting Help

New battery from the dealer costs about $200 (I googled it) and they will charge to install.

 

I have to push back again on the premature statements that the battery is weak. My experience on two Gen3s is that these measurements are nearly 'normal' on relatively young batteries -- my 2010 in winter at two and a half years, and even my 2012 at one year, specifically this afternoon merely an hour after an errand run of two hours roundtrip.

I don't have any mpg problems. The past cases of 12V-battery-related poor mpg were with much lower readings. At least one new reader was unnecessarily pushed to change the battery with similar readings, and it didn't fix her problem. And another reader posted this handy Prius 12V reference chart to another thread (sorry, I forget which):

Note that this scale applies only to Prius and its 12V batteries. My non-hybrids fail to crank on battery voltages that are perfectly acceptable in the Prius.

AliQS: How old is your 12V battery? Has it ever been changed before?

 

Each dealer is different, expect about $100 for labor. Always good to call around and compare prices. Sometimes there are service coupons in your area. See the Toyota owners link.


Toyota Owners Official Web Site: Service Coupons, Owner's Manuals, Service Scheduling And More

12v battery replacement cost | PriusChat

 

Your local dealer will probably charge you one hour of labor time to install the 12V battery. The voltage readings that you reported are sufficiently low that I suggest you have the battery replaced before the next winter - if you have cold winters in your area. The point of replacing the 12V battery is to avoid a no-start incident. It's not obvious that 12V battery replacement will help the symptoms listed in your OP.

Your original question was whether your car has a problem with the hybrid vehicle battery. Given the results that you've posted, it is possible that the hybrid vehicle battery has lost some capacity but the problem is not bad enough to turn on any warning lights. I wouldn't worry about this for now.

This table is incorrect as it relates to flooded lead acid batteries. Since the Prius 12V battery is AGM, 100% SOC corresponds to 12.9V. So as a rough index, add 0.3V to each row to determine AGM battery SOC. Further, I think that 0% SOC at 10.5V is too low, the voltage should be in the low 11V range.

 

fuzzy1, please note that I only stated that the OP's 12 volt is getting weak. I also stated that the battery would probably be Ok until winter time. I also agree that the voltage chart above applies to standard flooded batteries and not AGM type batteries.

And yes, some Prii do fine with weak batteries, when some other's suffer in one way or another.

I am waiting and hoping the OP will fill out the survey that is asked of new posters with MPG problems. I have also posted that link. IMO, I suspect the low MPG the OP is suffering from is being caused by more than one thing. Once the survey is completed, then all of us will have a better idea of what is going on and may be able to pinpoint the probable cause and needed fixes or repairs.

FWIW, a fully charged AGM battery in a Gen II Prius will read the following when the "test is run".

Accessory Mode: 12.6 volts or higher
Ign On Mode: 12.4 volts or higher
Ready Mode: 13.8 to 14.2 volts.

The OP has posted 12.2 11.8 and 14.4

What that tells me is that the battery is WEAK, and that the charging system is working overtime trying to recharge the battery. That does not mean that the battery MUST be replaced NOW. What it means is that it is getting weak, and sooner or later the battery will fail. When that happens, the battery will either have to replaced OR the Prius will need a jump.

It is simpler to change a battery at your convenience than it is to change a battery when it goes dead. Nine times out of ten your battery will fail when you need it the most. Either late at night or on a cold rainy/snowy morning.

Here is the link once again for the survey. I hope the OP fills it out.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

Ron

 

Well said Ron

 

First up, congratulations on following the instructions for measuring the 12V battery and correctly reporting all three values. You'd be amazed how many people can't follow those instruction and only report "it's ok, 14.2 volts" or something like that.

The most telling voltage is the 11.8 volts under light load (ignition on). This indicates that your battery is slightly weak and will probably need replacing soon. It is not so bad however that this alone is likely to cause any major driveability problems. So replacing the 12V battery wont hurt, but it may not make any difference to your particular issues either.

 

Now to your actual issue. It appears that everything here is linked to the relatively common problem of low of SOC (state of charge) during the first few minutes of driving whilst the engine is cold. The low SOC causes the gas engine to work harder, to power the car and also charge the HV batteries, so you'll also notice lower MPG during this period.

As you rightly suspect, aging and diminished HV battery capacity can exacerbate this problem, but it's not necessarily the only cause, and it's not necessarily a death sentence for the HV battery either. Other things can also contribute to draining the charge, such as heater, demister, aircon etc usage, and also poor health of the 12V battery (which can draw a lot of charging current during the first few minutes).

When you first start the Prius there is often a pretty large demand on the HV battery. The hybrid drive tries to minimize the loading on the gas engine for the first minute or so (while it's cold), so the electric drives take a lot more of the load. At the same time the 12V battery charging circuit may be demanding full power (particularly if your 12V battery is weak) and heat and aircon may also be going full blast. Many of us see a relatively rapid loss of SOC bars, and consequent reduced MPG, if driving off straight from a cold start.

A really good tip to ease the problem is simply to let the Prius sit in "P" for the fist 45 to 60 seconds after starting, and let the engine idle. (BTW, just pump to gas pedal once to start the engine if it doesn't do so by itself). Also, if at all possible, delaying the turning on of the heat or aircon etc for the first minute or so will really help out too. Please give these two things a try and report back. You'll be surprised how much difference it makes.

 

Again Uart is giving sound advice, but anything that makes the car harder to move means the engine, and particularly when cold "at first start up" the HV battery is worked harder to to remove the load from the engine to reduce emissions.

So please check those tyre pressures and report them here, and also the information on the new tyres as again surprising as it may seem the wrong type of tyre can also affect the charge in the HV battery along with increased fuel consumption.

John (Britprius)

 

Both points that uart and Britprius make are sound and valid. If the OP will fill out the questionnaire and post it, I believe we can get down to brass tacks. As I stated before, generally there is more than one thing that contributes to poor MPG on the Prius.

Ron

 

I found it cheaper to buy the Optima on line. Lower price, free shipping, no sales tax, no core charge is hard to beat. If you don't know what you are doing & don't have the right tools it is a 2 hour job. Feeling good because you did this yourself is priceless.

 

The 12v myth... I know I'm going to get a lot of hate from people who keep preaching the "it's below 12v...you need to get it changed." I have changed out over 10 aux batteries and have never noticed any change of MPG or problems on cars that had 11v+. ALL drivers reported the same mileage after getting brand new batteries(Optima, OEM) weeks...even months after.
The cars I have seen issues is with batteries under 11 volts. Drivers did not report MPG issues, it was starting issues and weird lights flashing on and off every once in a while. The biggest issue I ever saw the low voltage affect was error codes with the air bag system. Once battery was replaced, the errors went away.

Let the hate comments start now...

 

I am sorry that the experience of others is deemed to be hate in your eyes.

 

Hate in my eyes?? I mean people are going to start "bashing" me because they are so focused on the 12v thing.

 

Many folks 'know' how to tell when a 12 volt battery is dieing, it makes that grinding/groaning noise when starting the car. Sadly, no humorist at Toyota recorded that noise and arranged the computers to play it when the Prius 12 volt battery get low, so Prius owners never hear it, and never 'know' that the 12 volt is dieing until it has. (It is not that the 12 volt battery in a Prius lasts any shorter time than a normal car, it just gives less warning)

When coupled with the fact that one of many failure modes (one cell dieing) results in a large drop in MPG, the armchair experts here, like me, 'listen' for a set of symptoms that might mean the end is near for the 12 volt. I never recommend testing or replacing a 12v battery until they are already having symptoms. I hope you notice this title:
Weird stuff happening? MPGs dropping? Test The Battery | PriusChat
Mr. Schumacher is only suggesting testing the battery once you already have other symptoms.

The flip side of this is that testing is free, and Toyota dealers consistently fail at it, so it gives the car owner something to do. It would be fair to say we may over test the 12 volt battery of cars with symptoms we can't pinpoint.

I almost never mention 12v battery issues for a Gen 3 Prius unless they are already having to jump start it. 2007 or earlier, it is worth mentioning if the electronics are doing odd things. Next year I will consider 2008s suspect.

One time I AM adamant that owners change their 12 volt battery is once they have to jump start it repeatedly. Toyota has left the Inverter at risk if the owner reverses polarity during a jump start, and a new inverter is a multi thousand dollar part new. Even used is upwards of $500. If you have to jump it 3 times, replace it.

None of this is meant to behatred or bashing. It is concern that owners are not recognizing that their aged batteries (no 12 volt battery in a normal car gets much over 5 winters*) are impaired. Try using the power windows in ACC and in Ready, if they are slower in ACC, the battery is shot. It is true in any car, not just a Prius.

I am sorry that you view this concern for our collective inability to recognize a weak 12 volt battery as hatred or bashing of you. You might think "Why didn't Toyota have an alarm for a low 12 volt battery?", until you realize that such an alarm would be powered by the 12 battery it was trying to test. If they could do such a test during power up, we would have fewer stranded owners.

*How to extend the lifespan of your car battery | Fox News

 

I used to be in the it's under 12v replace group. Started experimenting with my customers that came in complaining about lower MPG. Some with perfectly good voltages and some with bad according to the "12v test" ALL cars had low tire pressure. Put some air and didn't change the batteries. MPG went back on all cars. Good and "bad" batteries. Hatred or bashing of me?? What are you talking about? I'm saying that some people are going to bash my post BECAUSE they are so focused on the 12v test and think that's the solution if the battery is low.

 

If I would have known that asking the OP to run the test would have caused this much hubbub in the group, I would have never posted it in the first place. I now see that I should have posted the link which I posted second and asked the OP to simply fill out the questionnaire.

I simply asked her to run the test since her car is seven model years old (2006).

I am still waiting and hoping that the OP will fill out the questionnaire. Then I believe all of us here will be able to see what is happening and hopefully help the OP resolve her problem.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

The OP has given us "some" information, but not enough to really properly diagnose the problem and correctly solve it. Until that happens, we can only guess and make assumptions. All we really know is the following.

When accelerating from a stop the mpg is in the single digits, whereas always in the past it would start in the teens and work it's way up as my speed increased.
There are fewer blue battery bars on the display.
As the car warms up, the mpg behavior also gets better and the blue battery bars increase.
The car has new tires on it with unknown tire pressures.
The car seems to show 60 MPG rather than 99 when coasting more often(not in S4 mode)
The OP is concerned that the traction battery might be failing.
The 12 volt battery is testing with lower voltages than a new battery would (weak)

I honestly don't see how any of us can properly pinpoint the correct solution without more information. However, once the OP fills out the questionnaire then I believe we will have the answer.

Ron

 

I will also add that I believe what uart said above explains a lot of what her problem could be, however I still feel there are other areas that might need to be addressed. Hence the link and the request for the questionnaire to be filled out.

Ron