How do you know if your (12V) battery is on its last legs?
 

I'll admit I haven't read all the threads on the 12V battery, nor really understand much about what it does, but, in a regular car, you can tell when your battery is going as the starter is sluggish, etc. You usually can tell (depending on the weather) when you're within a week or two of when it will die.
In the hybrid, (again, I'm not sure what the 12V battery does) are there any tell tale signs that the battery is dying? Does it have the same expected life as a regular car's battery (or is it longer as it doesn't need to turn over the engine to start)?
Thanks!

Re: How do you know if your (12V) battery is on its last legs?
 

it is nothing more - nor less - than power storage for all the electronics. look at it as back up power supply. has NOTHING to do with starting engine.

yes, esp if you have nav system. if you do, you can log into data display. there are several data displays, one of them will show you battery voltage. if it's below 12V, charge it. it should be in the area of 13+ - 14V after charge and stay there for extended time. if it quickly drops down - well, you got it.

I had mine charged last year, it showed 14.3V as a result.

If you do not have nav system, tough. you can take it to say Autozone, and they will tell you this or that about its state, but keep in mind - as I am in real good standing with my local O'Reilly guys here - they plain told me, their testers are not made for deep cycle batteries. There's a very complex procedure, wit plotting results, to determine health of a deep cycle.

I'd say, to keep it on the safe side - replace it after 7 years. mine will be there next year.

Re: How do you know if your (12V) battery is on its last legs?
 

Thanks, so without the NAV system, there's no way to know, is there? Will car still start if 12V is dead? I'm a bit confused, what happens if the 12V is dead? (sorry for being dense)

Re: How do you know if your (12V) battery is on its last legs?
 

Most likely if the 12V is dead your vehicle will not start. Remember it powers the electronics required to start the vehicle, although it does not directly supply power to the motors it is still required in the start process.

Re: How do you know if your (12V) battery is on its last legs?
 

Thanks...thus my original question.
With an ICE car, if you start it with a dying battery, you'll hear it sluggishly struggle to turn the engine over.
With hybrids...what happens, you show up one morning and the car is totally dead? My point is...are there any leading indicators or is it just "sorry Charlie"?

Re: How do you know if your (12V) battery is on its last legs?
 

nope. it does not have starter. it starts off hybrid battery. electronics do not permit that battery to fall below a specific charge level, they will turn ICE on and recharge it.
if you car is d-e-d - dead - you have to tow it to dealership for them to charge hybrid battery and then you can go back to using it.
you can only approximate 12V battery condition. like I said - and I spent quite some time researching same question - you have to have special equipment to properly load test deep cycle battery.
like I said - sorry for broken record - for the heck of it, replace it at about 7 years. I came across post somewhere at Toyotanation, from end user, who had his 12V die on him twice - and he simply recharged it and drove the car. so, it's not a catastrophic failure. catastrophic is when hybrid battery goes boink.

Re: How do you know if your (12V) battery is on its last legs?
 

Urkoz:
Dealer said this can't be done with my 2009 tcg navigation screen. How do you get the data screen?

Thanks,

PB!

Re: How do you know if your (12V) battery is on its last legs?
 

Inquiry was to Urokoz's post about reading the voltage on the 12 volt battery on the navigation screen. Into the learning curve on this site.

PB1

Re: How do you know if your (12V) battery is on its last legs?
 

I DO NOT BELIEVE that you can get into diagnostic mode on 07 models, and can NOT on 09 or later.

I can speak only for ones with nav unit - and just did it again. mof, I have entire write up posted back here (why there's no sticky-s here anyway?) on how to

press power button once>press and hold info button>start flipping light switch all the way forward-back> in 4-5 flips, diagnostic screen comes up on nav unit.

there's also way to test sound system and buttons on steering wheel. something about pressing 3-6-9 or some like that on nav keypad.

Re: How do you know if your (12V) battery is on its last legs?
 

I have had two 12 volt batteries die in three years. Lucky they were both under warranty. Vehicle will not start when the 12 v battery is dead. You will need to jump start it. Measuring the voltage, the 12 v battery will show less than 12 v. I can't remember the minimum voltage before it will not start. After jump starting, if the vehicle is run, then it will charge up. However, if the battery discharges faster than before when vehicle is not used, ie overnight, then it is a sign that the battery is on its way out. The dealer can check to see if the battery can hold a charge.

My vehicle was purchased new, but about 9 months after the manufacturing date. The first battery probably sat for a long time and went through several discharge cycles. It only lasted about 2 months after purchase. Can't really blame anyone for that one. Dealer said that the 12 v battery is used to power the computer, thus has about 1/2 amperage as a regular battery (somewhere around 300 amps maybe). If you drive frequently, then it is not a problem. If you drive infrequently, it might pay to hook up a battery tender (designed for AGM batteries) to keep it charged.

I don't think the battery wears out any faster than a regular battery. Just that if you let the car sit for long periods without use - several weeks or more, then the battery will discharge. It powers security and other electronics with low voltage while the vehicle sits, so there is a small drain even when the vehicle is shut off.

Re: How do you know if your (12V) battery is on its last legs?
 

Great, thanks!

Re: How do you know if your (12V) battery is on its last legs?
 

hey, haroldo, check this out:
http://www.batterymart.com/p-Mega-Cr...M-Battery.html

it is cheaper and has better specs than yellowtop Optima.

Re: How do you know if your (12V) battery is on its last legs?
 

or this:

exide Orbital Orb34m-36 Sealed Maintenance-Free AGM Marine RV Battery

$139 online
The Exide Select Orbital marine batteries are a complete line of hi-tech sealed batteries, designed to meet the needs of the serious marine or RV battery user. These advanced-design batteries use ultra-thin high purity lead plates. This design allows us to give you some of the lowest internal resistance batteries available. Absorbant glass mat technology gives you a completely sealed battery that cannot leak in your RV or boat. The Exide Select Orbital marine battery can be mounted anywhere, in any position in your RV or boat - they do not leak or spill like normal batteries.

Re: How do you know if your (12V) battery is on its last legs?
 

Used Urkoz's method to access that part of the Navigation with various display functions. But no info on the 12 volt battery. Had the car at the dealer and the service rep said they do a 12 volt battery check every time it's in for service. It's a test with load and printout. Battery checks out good. No charge.
Urkoz. My thanks for your help.

Re: How do you know if your (12V) battery is on its last legs?
 

no problem. you simply didn't get to the right screen. that sh-t is quite convoluted.
also, keep in mind, you can much so adjust microphone sensitivity form diagnostic mode.
dealer bs-s you. have my word, they don't load test battery every time.

Re: How do you know if your (12V) battery is on its last legs?
 

go here:
http://i49.tinypic.com/2iqjy3b.jpg
and hit vehicle sensor check
as you can see, mine is not doing too good.
http://i50.tinypic.com/2ibn9q9.jpg

Re: How do you know if your (12V) battery is on its last legs?
 

charging as I type. will prolly replace it in week or 2.

Re: How do you know if your (12V) battery is on its last legs?
 

What is the minimum V on the AGM battery (per the nav screen) before it may be best to change it (without waiting for it to not start first!)?

-- Alan

Re: How do you know if your (12V) battery is on its last legs?
 

Using the scan gauge set to read the 12 volt battery. My '07 TCH read 11.5 volts after letting it sit at home the day before.

The new XLE hybrid reads 12.5 volts after sitting at home all day the day before. The 12 volt battery powers the ECU even when it's in the sleep mode. Some techs call the 12 volt battery the instrument panel battery. It may power the headlights, instrument instruments including the lights, radio, heater, AC and heater fan. The AC compressor does get it's power from the traction battery.

You can also use a voltmeter set to the 15 or 20 volt DC setting. Read the voltage across the terminals of the 12 volt battery (with the engine off) red probe to the + terminal. Best to take the reading after the car has sit all day or all day the day before. The ECU in the sleep mode puts a very slight drain on the battery and will help you get a more accurate reading.

Re: How do you know if your (12V) battery is on its last legs?
 

I read somewhere, where I learned about disgnostic mode, that if battery reads below 12, it's a goner and needs to be replaced. so it will be.

Re: How do you know if your (12V) battery is on its last legs?
 

From the service manual:

Standard voltage:
11 to 14 V
If the voltage is below 11 V, recharge or replace the battery
before proceeding

Re: How do you know if your (12V) battery is on its last legs?
 

I don't know about that, mine read 11.5 volts for about 1 1/2 years and was working fine till I traded my car off. It may have been weak, but the car was almost 5 years old. The car was sold as certified used car by the dealer so they may have replaced it.

Testing for a going bad battery is usually 10% of it's normal voltage. A 12 volt battery less 10% would be 10.8 volts. Your right, toyota says 11 volts, time replace it.

Re: How do you know if your (12V) battery is on its last legs?
 

11V sounds great to me! My '07 reads 11.5 after sitting a day. It is the original Panasonic. Going in for my 75K service this morning, and will verify with them that 11V is the recommended replacement threshold.

-- Alan

Re: How do you know if your (12V) battery is on its last legs?
 

Just got back from the dealer. He told me my battery is below 300 A capacity, and needs to be replaced. I declined his $450 quote for the battery replacement. I picked up an Optima Yellow Top For $230, and have a $25 rebate to send in.

The battery swap was easy. However, now my car says "Service Hybrid System" with the red "!" warning light staying on. Does anyone know if this will clear itself once the settings recalibrate (assuming nothing else is wrong)? None of the nav screen diagnostics identify a problem or will reset this dash warning. Everything seems to be working fine.

For others doing the same swap, note that there is a thermistor over-temp sensor is under the original battery label. Just pull back on the label and the sensor pulls out easily, and then can be pressed snugly under the top clamp against the top of the new battery.

-- Alan

Re: How do you know if your (12V) battery is on its last legs?
 

Hey Alan,
Thanks for letting us know. Did you figure it out how to clear the errors?
What tipped you off that you need to replace the battery besides going to the dealer?
I have a 2007 camry hybrid made in japan and has about 108,000 miles on it. Do you think I need to replace it soon?

Re: How do you know if your (12V) battery is on its last legs?
 

Mine is also a first month, Japanese made TCH, and I live in the Sonoran Desert (Phoenix area).

The error finally cleared itself last night on my way home. Took about 30 miles of driving, and it just went away.

My clues that I may need a new battery were varied. First, many of my Toyota hybrid driving friends (Camry, Prius, Lexus) are replacing their AGM 12V in 4 to 5 years, and I know of nobody who lives out here who got more than 6 years. Second, the discussions here indicated the 12.6V battery should not fall to more than 11V after sitting a day or so. Mine was getting close to that. Third, the dealer said the cranking amps of the battery was about half its spec, and that it was probably only a short time to failure (he suggested weeks to maybe a few months).

I just decided to do it now, in part because my local AutoZone had the Optima Yellow Top at $10 off, and there was a $25 factory rebate, and I didn't want to wait until it wasn't my choice and it was 115 degrees!

-- Alan

Re: How do you know if your (12V) battery is on its last legs?
 

that's why you use back up battery, to feed power to the system, when swapping out those batteries. may be pain in too-too to do, but saves you headaches later down the road.
service light should go away after 3 consecutive startup/shut downs are performed.
when I'll be swapping mine, I'll have jumpers connected to cables and back up battery in the trunk. have not figured out yet how to connect them, but will.
yes, we do know about thermistor. it's pried off with a screwdriver and then placed onto a new battery.

Re: How do you know if your (12V) battery is on its last legs?
 

oh, and btw. Sam's has Optimas for around $170.

Re: How do you know if your (12V) battery is on its last legs?
 

I took a bench power supply I have and clipped it to the old battery. Then I lowered the voltage until the current was zero (matching the old battery voltage). Since the car was in use all morning (charging the battery), the then resting voltage was 12.1. I unclamped the terminals from the battery, with the power supply clips still on the car cables (and the power supply current jumped to around 100 ma). Then I attached the cables to the new battery. Not sure exactly when, but before I had both cables on the new battery, one of the power supply leads fell off! Oh, well.

-- Alan

Re: How do you know if your (12V) battery is on its last legs?
 

The 100 ma drain is really low and probably caused from the sleeping ECU. Makes it easy to see why you can let a toyota hybrid sit for a few weeks and it will still still start right up.

Re: How do you know if your (12V) battery is on its last legs?
 

that's why I said - I'll have to figure out how to connect jumpers to cables so that they DO NOT fall off during all the manipulations. not that simple, actually, as for regular jumpers, there's not enough room inside the battery compartment to hook them up. small jumpers may not have enough grip on the jaws to stay on. may end up removing insulation somewhere on the cables for hook up, and then covering it with electrician tape.

Re: How do you know if your (12V) battery is on its last legs?
 

I can assure you the car won't start with a dead or mostly dead 12v battery. Voice of experience. :D

Yesterday evening I went to start the car and the battery was pretty low. The car tried to come on, but after a point the info display in the gauge cluster start going on and off and saying to check the VSC system when it would come on. Some of the other lights flashed too.

I put it on low power charge on the charger for a couple of hours and the car started after that, then I drove the car to let the car's onboard system charge the 12 volt some more.

I'm replacing it with an Optima tomorrow. I'll report back how it goes. I don't anticipate too much difficulty.

Re: How do you know if your (12V) battery is on its last legs?
 

I forget if the 12 volt battery in the trunk has side or top terminals. I was thinking cleaning the terminals might help the low voltage if they are on top. Another way to read if the battery is low, is to turn on the headlights for 10 to 15 minutes (engine off), then measure the dc voltage across the battery while they are still on.

The new Optima will sure cure your battery problems.

Re: How do you know if your (12V) battery is on its last legs?
 

FYI, from dealnews.com:

For in-store pickup only and with limited availability, Advance Auto Parts offers the Optima YellowTop 12-volt AGM Car Battery for Toyota Prius, model no. DS46B24R, for $124.99 via the directions below. That's $1 under our mention from six weeks ago (which included free shipping) and the lowest total price we could find by $40. Sales tax is added where applicable. Rebate expires May 31. To get this deal:

Add the Optima YellowTop AGM Car Battery to your cart for $199.99
apply coupon code "VISA" to cut it to $149.99
redeem this $25 rebate for a net price of $124.99

Brand: Optima
Model Number: DS46B24R

Re: How do you know if your (12V) battery is on its last legs?
 

The 2012 Owners Manual says the following about the 12V battery in the specifications:

12.6 -12.8 V Fully charged
12.2 -12.4 V Half charged
11.8 -12.0 V Discharged
(*: Voltage checked 20 minutes after the engine and all the lights are turned off, at 68 deg. F)

It would seem to me if you were consistently getting Half Charged range when you test with a multimeter, I would start to get concerned. If you then check voltage when the car is running and hopefully charging, I would expect it to be up around 14-14.5 volts. If it does not come up to that, then you can suspect the charging system.

Another way to evaluate the state of a lead acid battery if it has removable cell caps is to measure the specific gravity with a battery hydrometer. They are relatively cheap. If you have a suspect battery, you can confirm it by testing each cell to see how uniform they are. Often you will find one cell is lower than the rest. The only trick of this test is making sure you don't get any acid on your car, hands, or clothes!

On buying a replacement, cranking amps or CCA is irrelevant as this battery is not used for starting. Buying a deep cycle seems to make a bit of sense as there does seem to be a drain on these batteries when the car is not running. Generally you can tell the capacity of a battery for deep cycle by the amp-hour rating, or the reserve minutes. More is better.

Consumer Reports I recall used to test Optima and recommend them, but in the latest tests they do not seem to be included. DieHard Gold and Platinum seems to test near the top in most sizes.

Does the original battery have a vent connection? Venting of the hydrogen and oxygen would seem to be a bit of a concern as it is located in the trunk rather than under the hood where there is lots of ventilation.

Re: How do you know if your (12V) battery is on its last legs?
 

After a little more research, I believe the OEM Toyota 12 volt battery is a gel type. If so, there will be no way to test the electrolyte specific gravity. I found this graph that shows a bit more accurately what battery condition is based on voltage. It says it is based on no load and a 3 hour rest after charging. Without disconnecting the battery, you can't assure no load, but perhaps the idle drain is low enough that the values still apply.

Expected life of a gel type should be good, unless it has been overcharged. They are more sensitive to charging voltage. That is probably why Toyota recommends no more than 5 amps for charging.

Re: How do you know if your (12V) battery is on its last legs?
 

The 12 volt battery is the power source for everything in the car that uses 12 volts. Most important for starting would be that it powers the ECU. The ECU in turn connects the traction battery to start the engine, sometimes rolling the car to do so, only if you put it in drive or reverse quick enough.

Batteries are usually not usable if they are 10% below their rated voltage. That would be 10.8 volts for a 12 volt battery. If you can't get your car to start due to low illuminated instrument panel. Make sure everything is off, including closing the doors so the dome and map lights don't come on. Let the car sit for 3 to 5 minutes. Sometimes this makes enough difference to get the car started.

I think it was haroldo that long time back said, be sure the clock is black or not illuminated when you get out of the car. To turn if off, press the power button till the clock goes dark. I do this with my '12 TCH but also sometimes see the mid reminding me to turn the power off.

I understand the deep cycle 12 volt battery in the trunk is vented down and outside the trunk.

Re: How do you know if your (12V) battery is on its last legs?
 

Sorry to be waking this thread up, but I have been thinking I could connect the backup power cables to the points under the hood before changing out the battery. Does any one have any concerns with this approach, aside from having to be careful with the positive cable end in the trunk not touching any conducting material in between the battery change?

Re: How do you know if your (12V) battery is on its last legs?
 

Should be fine. Just check that when the car is turned off that there is still 12 volts at the points you choose under the hood. In any case I think all the "problems" caused by disconnecting the battery is just internet mythology.

Re: How do you know if your (12V) battery is on its last legs?
 

My backup power source did accidentally disconnect for a few seconds, and that left my computer "dumb." It was a number of complete start-up cycles with cool down before the engine light reset itself, and more than a tank of gas before fuel economy returned from normal (it never got real bad, though). All radio settings had to be reset, and a few other settings in the car reverted to factory default. Not a myth in my experience!

-- Alan