12V Battery Voltage in Diagnostic Display -- New Battery Needed?

new is around 13 volts. are you driving much? maybe charge it up and keep an eye on it

i think there is a 12v warning, but doesn't seem to work well. the fact that your car starts may be the problem

 

I bought a new battery from the dealer a few weeks ago and checked it before I installed it and it showed 12.55v with a multimeter.

 

put a charger on it, then see what it holds at over time.

 

The number shown on the MFD tends to be a good fraction of a volt lower than what you would see with a meter on the battery itself.

The numbers you are showing are pretty much comparable to what I was seeing for the last four years of the ten year life of the battery I just replaced (I'm not saying the numbers were higher for the first six years, I just didn't own the car then), and I'm pretty sure if I walked outside right now and checked with the one I put in brand new this winter, it would look pretty much the same.

Edit: just for grins, I did exactly that, and mine read 11.2 on the MFD in accessory mode, rising to 14 once in READY.

I did not bother with a meter on the battery itself, but my ScanGauge (which sits within inches of the MFD, but is measuring the voltage on a different circuit, the one that comes to pin 16 of the DLC3 port) was reading pretty much exactly 0.7 V higher than the MFD the whole time.

If your battery isn't giving you some actual reason to worry about it, I'd probably worry about something else.

 

Best to read independent of the car's displays, at least the voltage, with a multimeter, or better: voltage and CCA with electronic load tester. Just happened to be doing the latter today:



Automotive retailers selling batteries will often have pro-level testers of this ilk, and will test for free.

 

Hey guys, I have a 2012 Prius C which has never had the 12V battery replaced. Lately I've found that the car has trouble turning on, but only when cold. After discovering this diagnostic mode, I noted the following battery readings from the Vehicle Signal Check Mode:

1. Engine cold and OFF, headlights OFF = 9.7 V
   
2. Engine cold and OFF, headlights ON = 9.4 V
   
3. Engine ON, headlights OFF = 15.6 V
   
4. Engine ON, headlights ON = 15.5 V
   
5. Engine warm and OFF, headlights OFF = 12.5 V

So if I understand correctly, the first 2 readings confirm that I need to replace the 12V battery, does that sound right?

 

It very definitely means that battery needs to be charged! It's well below what's normally considered full discharge, which would be around 10.5. COVID has been discharging batteries all over.

If you put it on a nice 4 or 5 amp charge for a solid day or so, then check its performance again, it might be ok. Or it might not.

Some posters will say being that far discharged will always do some damage, which is true, but sometimes it isn't much damage and sometimes it is. If you just see how it checks out after being fully recharged, you can then decide whether it needs replacement or may serve you well for a while yet. Mine needed replacement at ten years, and it had lived through at least a handful of occasional unintended deep discharges.

 

Do yourself a favour and check the voltage independently of the car’s display, with a digital multimeter. Cheap ones can be picked up for as little as $20. For more definitive: an electronic load tester. A lot of automotive retailers have pro level testers of that ilk, will test for free. Dealerships have them too, but will likely charge you (pun) for testing. Or pick up a prosumer level tester, say Solar BA9.

That said, 8~9 year old battery? Just change it for chrisakes.

 

Yes absolutely.
AND just the age confirms it too.

 

If you're looking at the MFD display and seeing something like, say, 11.9, and wondering what that means, sure, do the independent test with a meter, it will tell you how much lower the MFD reads in your car. Most I've seen are low by a good fraction of a volt, so you might end up deciding there's no concern after all. (You can also make a mental note of what the difference is; it never seems to change much in the same car.)

On the other hand, if you are looking at the MFD voltage reading and seeing 9.7, you've probably seen as much as you really need to.

 

I am not sure if it is a concern or not, but 15.6 V looks a bit high to me. I typically see the charging voltage around 14.7 - 14.8. Maybe the charging voltage is adjusted for temperature, and Toronto is really cold these days.

 

So I’m looking into some installation videos to see if this is a job I can do myself. I’m not a car person at all but have been able to do some repairs on my own through YouTube, such as replacing my headlights with led bulbs.

I found this video on replacing the high voltage battery on a Prius c. It starts with removing the connection between the 12V battery and the HV battery, and also removing the big orange circuit on the HV battery. I haven’t seen this on other videos which talk about replacing the 12V battery though. Is this recommended, or not necessary at all for the 12V replacement?

 

i'm not sure what your question is. if you're going to replace the hybrid battery, start by disconnecting the 12v.
the only reason to replace a 12v is if it won't hold a proper charge anymore.

 

Conversely, if you're going to replace the 12 volt battery, you just do that, as you would in any other car. The job doesn't involve the traction battery in any way, and you don't need to do anything with any orange plugs or wires.

 

Thanks! I’ve never replaced a car battery before so this is all new territory for me. But I’m gonna watch a bunch of videos and read more posts here bc I think this is a job I can manage by myself.

 

Disconnect neg first, reconnect last. Lightly sand the posts of new battery prior to install, with fine grit sandpaper strip*. Run a wire brush through interior of cable clamps.

if possible run a full charge session on the new battery, with an appropriate smart charger (see Owners Manual for max amp, 4 is likely good guideline)

When installing the clamps snug their bolts firmly, but “don’t go mad” (as the Brits say). One-hand it with a small box wrench helps to limit torque.

Reinstall vent tube and hold-down bracket. A few washers may help if the bracket ends up “tippy”; it’s a poor/finicky design.

*avoid breathing the dust, wrap and dispose the strip.

 

I ended up buying the Group 51P for Toyota Prius AGM battery from royalbatterysales.com:
StackPath

Model: 51P-TCAGM
Description: Group 51 with JIS pencil posts AGM car battery for Toyota Prius

And here are some pics. Anyone have experience with this battery? I hope I bought the right one!

 

Does it fit Prius C?

 

It’s actually about an inch longer than the stock one... got it installed and working in my Prius c, but now having trouble getting the holding bracket back in place. Wondering if I can do without it?