Is my 12V battery dead?

If you have access to a voltmeter, check the voltage on the 12V AuxBattery, then do the same check with the battery under load (…e.g. with headlights on). If you haven't the sllightest idea of what I'm talking about, drop by your local Toyota dealer (…or Autozone) and ask them to do a load-test on your AuxBattery. Some places will do a load-test for free, others might charge you. Good luck!

 

I'm not sure, and am always sceptical about using the car's diagnostics, too many variables. Would suggest:

Check the at-rest voltage with a multi-meter first, with the car off. Do you have the jump start point under the hood? some of the early c's didn't. So, either directly at the battery, under the back seat, or under the hood. If you get less than 12.5 it's borderline. Less than 12.4 some intervention is needed, say at least a charging session.

Better than a voltmeter is an electronic load tester, like Solar BA5. It'll check the voltage, plus the CCA, and make a rudimentary diagnosis, either good, good but needs charging, or failed.

If you don't want to spring for such a tester, or even a multi-meter: any decent battery retailer should have a pro-level electronic load tester, can test it for you. Likely gratis.

 

Hmmmmm....Canada, winter, three-year-old battery....it's possible.

As the previous poster said, down here in the US you can go to an auto parts store and many of them will test the battery for you.
Of course..............they also SELL batteries, which is sort of the whole point.

I would strongly recommend against visiting a dealer (yet) unless your car is still in warranty, and unless Canada has much stronger consumer protection laws that we do down here....

 

What are temperatures like, can you be more specific about your location? Especially on short trips, where the car is partially warmed, the car is aware of the ambient temperatures, and is going to keep the engine on more ambient temps drop. You note though, that shutting off the heat/vent system, the engine still runs. I've found at red lights that's one thing that can tip ours to shut down, in similar scenario. The more it warms the more it gets back to normal too: shutting down regardless.

 

G'day upthere,

While we downunder are looking for our first heatwave of the year today (through to next week), your concerns about the 12V battery and the cold weather you live with, made me wonder if anyone has one of the multifunction accessory-adapters that as well as offering a plug-in USB charger will display interior temperature and the voltage of the 12V battery. Well, that's what the suppliers are claiming.
As an example, not a recommendation, I've copied a quickly found link to such a device:

Car USB Charger Voltmeter Thermometer Sale - Banggood.com

I'd be interested to know if these cheap devices could help you watch the 12V battery status with a minimum of fuss.
David S.

 

That would be of limited use on the Prius C because the 12V power outlet is turned off when the car is turned off, and when the car is turned on the high voltage battery charges the 12V battery. So it would be like trying to test the battery of a car with a standard gas engine while the engine was running - you're not really testing the 12V battery but rather the thing that's charging it.

 

G'day Sean,

Thanks for the feedback.
What about if the car is only turned on in 'accessory mode'? I'm thinking if the 'Power' button is pressed without a foot on the brake pedal?

[Wimp mode ON] Too hot (33 real degrees and climbing ) at the moment to go outside and check in the Prius if I've got this process correct.[Wimp mode OFF]

I don't have one of these USB multifunction adaptors to test out so I'm speculating while awaiting info from anyone who does have one.

David S.

 

the best way to keep an eye on your 12v is with a simple digital volt meter at the jump post under the hood. every few months is plenty, especially when newer, and not having been drained.

 

Ah, yes - good thought. I just tried that with my 2012 Prius C and if you turn the key to the "accessory" position it does power up the 12V socket. And the "Ready" light does not come on, which to the best of my knowledge means that the high voltage battery is disconnected - so it would be just the 12V battery supplying the power.

 

This is what I have, it is connected to the 12V power port. You can identify a baseline voltage after leaving the car switched off overnight (say 11.5v or something) that is measured when the car is on Accessories mode. As the battery gets weak this value will reduce. So when it is around 10V you can change the battery.

​

 

I'd second @bisco: get a multimeter and check the voltage with everything off. Lots of other uses for such a meter, automotive and what have you: it's good to have.

 

G'day,
I decided to try a couple of cheap (ebay) accessory-plug-adaptors that as well as having two USB 5V sockets, claimed to have a sequential digital display showing the battery voltage, the amperage being drawn through the USB sockets, and the ambient temperature inside the car.
These arrived from Hong Kong yesterday and I've now tried them in my Prius c. Parked.
With the Power On in engine-on mode (foot on the brake), the voltage display was 14.4V which is probably due to the 12V battery being charged by the car system.
With the Power On but not the engine (I pressed the Power button without my foot on the brake), the voltage display was 12.4V. This seemed reasonable as the car had not been driven since yesterday.
The temperature indicated during the cycling of the three readings (about 5 seconds for each) was reasonable as well (about 26C).
One of the USB 5V charge outlets also worked charging my android phone during a short drive.
The one drawback is that the V-A-degreesC display is not easily visible to the driver due to location of the accessory socket in the Prius c (see phone-photos).
So, despite that, this looks like this may be $10 well spent. No idea how long the adaptor will last, of course.
The other adaptor will be tried in our 10-year old Yaris which is not getting much of a work-out at the moment.

 

I had a lot of IC engine running the other day, and I was wondering what was up..
Read here, and decided to measure the 12v.. Sure nuff, 11.7vdc and 11.0vdc with the headlights on..
However, since last Monday, I've been making short trips.. 3 miles park for 3-4 hours, come home 3 miles..
Doing about that without any long drives at all.. Can't be good for a 2012 battery..

 

Our use is sporadic and often short trips. If it's likely to sit several days I hook it up to an automatic charger and just leave it connected till we next use the car.

 

My charger is on the AWD RAV4, because it only gets used during winter snow storms..
Right now, it looks like another winter snow storm is on the way..
So, we won't be using the Prius for a couple of days..

I'll have to look for some DIY info on installing a new battery. Saw one on Amazon..
Optima Batteries 8171-767 (DS46B24R) YellowTop it might be the right size..

 

With the storm fcast over the next 36hrs (see above post!) and no planned errands The ChuggyPig is nice and snug in garage with battery-maintainer connected to 12V AuxBattery! (...just sayin')

 

Were you able to figure out what was causing the engine not to go into ev while idling or on stop?

 

*sigh*
Since this forum is mainly US, I assume those temperatures are Fahrenheit?