My 12v Battery Voltage Readings

When did you get that 12.22 volt reading? Had the car been sitting for a few days, or no more than 24 hours? If the latter, it doesn't bode well. Especially if there's been no "incidents" lately, ie: a door left ajar overnight, something like that.

Doesn't hurt, ever, to invest in a smart charger, see what it can do. You'll find lots of use for it, down the road. Give it a try. A typical smart charger will have some sort of indicator, let you know when it's done, satisfied with the battery's state-of-charge. If that does happen, then continue to monitor the voltage for ensuing weeks, see if it holds at higher level, or backslides back down to 12.2'ish. If the charger just keeps charging, charging, never indicates finished, or indicates the battery's bad, at least you'll know.

Either way, I'd start researching replacement batteries.

 

you quoted mendel, you got mendel. does it get any better than that? try that with your doctor or plumber.

 

Actually, even after 3~4 days, I've never seen 12.2 volt in a healthy battery. Again, try a smart charger, just for the heck of it, it'll pay for itself down the road. It might revive it.

 

Mine runs that all the time. I don't think the measurements are that accurate that one should panic over. Heck, the current owner of Pearl, last spring, was seeing 10.5V and the car was still starting just fine. I had to browbeat him into buying a new 12V battery.

To the OP, the car won't die while driving. If the battery fails it just won't get to "ready". A simple boost at the boost point under the hood will fix that. Get yourself a "booster pack" or even just an alarm system 12V gell cell battery if you're worried. You'll need two "test leads" that will connect to the alarm battery (1/4" blade push-on connector) and electronic type alligator clips on the other end. Best to use the insulators over those. DO make sure you get the polarity right if you do use the boost point (or on the battery).

 

12.56 with an overnight sit, right after charge, is still kinda iffy. I'd continue to monitor over the next days, weeks, and research replacement batteries.

If you DIY the swap charge the new battery before install.

 

agreed, check it every few days until you're comfortable.

 

On the other hand, mine has been right at 12.5 V for 5.5 years, and shows no signs of giving up yet...

 

Trying to determine if I have a failing 12V battery. I bought a Solar BA9 battery tester, and here are the results this morning cold. (Not cold outside, but car not started yet today.)

Voltage: 12.3V
Cranking Amps: 290
SOC: 62%
SOH: 97%
Resistance: 10.46m-ohms
Message: "Battery OK -- Needs Charge"

Based on what I'm reading in these posts, it seems like my battery is on it's way out based on low voltage? Every morning when I power on the car, the engine goes on. I assume the battery is low every morning, and that's why the engine is running? Also, wondering how a battery in this health is impacting my MPG?

 

Did it show the Cold Cranking Amps?

 

Oh yeah, 290 cranking amps

 

After looking at the Solar BA7 and BA9 I see both list capacity for up to 1200 CCA
guessing CA = CCA in the post above, although they are different measurements. blah blah

here is one persons take on the MPG issue, along with other 12 volt prius resources and a replacement battery recommendation.
Effect of the 12-Volt Auxiliary Battery on Prius Gas Mileage - Arnold Solof

 

This would also be my conclusion based on the numbers you listed above it. The battery is OK. It is just not fully charged.

Why? It just needs to be charged. If I was a bettin' man, I'd bet that you're making short drives and not giving the car time to recharge the 12V battery. If so, it might help to put it on a trickle charger now and then. Either way, though, if the SOC of the 12V get low, the DC/DC converter will increase its charging rate. As the 12V fills up, the charging rate will be reduced to protect the battery. A trickle charger will help keep the battery topped of and it'll last longer and you'll get slightly better gas mileage.

The engine is running because the car is programmed to start the engine a few seconds after putting it in ready mode. If there is plenty of charge in the traction battery, the engine may start later, but it'll still start pretty soon after you get rolling even then. If the traction battery is low, the engine starts up quicker. None of this has anything at all to do with the 12V battery.

If the 12V is low, the charging process will burn a little extra gas and affect gas mileage. But if you're making short drives, you get a double whammy. The short drives just murder fuel economy on their own, and to add insult to injury, there's the extra work of not getting the 12V filled up and therefore not getting to rest from charging it. But that's insignificant compared to the penalty of not getting to put any miles on a warmed up engine.

 

Most drives are 15 to 75 miles. I just drove about 30 miles today. Car rested about 15 minutes.
Voltage is now 12.2V. I'm not exactly convinced that I need a battery charger yet. If it's a good 12V battery,
then doesn't the traction battery keep it properly topped up?

 

Spec is something like 325, for the OEM IIRC. A new battery with that spec will ALWAYS read significantly higher, say at least 350, or more, and stay there for most of its healthy life.

290 says to me it's on its way out.

I would get new battery AND a good smart charger, to maintain the new one and/ or recover from "incidents".

With COVID times, and both my wife and I retired, ours spends more time on the charger than off. If we drive one day, then the next day we aren't, on goes the charger, and it STAYS on till next time car is used. I'm using CTEK 4.3, with quick connect wired in.

Excuse the CAPS, just a pain to change text to italic on a phone.

 

Drives that long should charge the 12V with no problem. But the Gen 4 doesn't charge very fast or hard.

My battery (the original) is often down around 12.3-12.4 V on the rare times when I check it in the morning. I've never had a problem with it. Part of the low reading is that the headlights stay on for 30 seconds after I shut down in the garage. Even under 12V, the car should start fine. Are you actually having problems? 14.53V when in READY mode shows that the car is charging the battery. If the car starts, I don't see a problem. Your numbers are pretty close to what I see on mine and I'm not having any issues at all. I do know, though, that in this FL heat, I'll likely be needing a replacement 12V within the next year. Since I have a lithium jump pack in the car, I'm not concerned about replacing the battery before it fails. Lots of people here on PC really obsess about the 12V if it's not 100% charged all the time. Unless the battery keeps getting lower and finally fails to light up the computers, I don't see anything to be very excited about.

 

It seems like we've taken a hit on mpg. We used to get over 55mpg easy around town, city driving. Now, I'm lucky to break 50 city. I hear a good deal of folks are getting better mpg's after a 12v battery change. You have a Prime, and I don't. Looks like your getting 100mpg+. You must be taking short drives with plug-in power. I probably can't really compare your mpg experience to mine in this situation. I'm not sure. Thank you for your time, and analysis.

 

Thank you. This makes the most sense to me. Just wondering if I can look forward to a noticeable bump up in mpg w/ new a 12v?

 

Gen 4 is still a bit more of an mystery than gen2 and 3. Some of that is due to many of the more technical members recently moving on to Tesla along with a lot of the more technical discussion. The rest I attribute to many new less technical people buying in as demand for ph-EV grows.

Jerry's post about the 100 mpg for a 13 mile trip ( important metric ) is in Mildreds gen4 prius (not a prime), but a newer and different model than your 17 three touring and a much different part of the US, topographically anyways.
Being in SCal there are unique issues out that way that contribute to lower mpg generally. It might take a few pages of discussion just to get some of them mapped out.

With gen4, my take so far anyway, not many of us fully understand how the electrical systems work as a whole. It's a fairly complex machine with many new subsystems added.

I'm noticing personally a lot of reports of the 12 volt running low specially in the prime. but other gen 4 too.
With mine I've seen a low voltage down in the 12.1x area. Although not often and it (the 12 volts voltage reading) bounces around a lot more than I'm used to seeing in previous cars owned.
And I still consider the cars 12v healthy, but questionable.
Plus not all multimeters are created equal and a couple 10ths of a volt, up or down, difference between any two, especially the less expensive ones, even of the same make and model is not unheard of.

Plus, toyota part numbers keep changing, even more so than in previous generations as I found out trying to get a part # and spec on the OE 12 volt for your model,, as well as the correct parts for my car the first time around, even using the vin check feature on some OEM parts sites.

Dang, that's one heck of a lot of excuses...

None of the above discounts the fact that: a weak 12 volt battery has a definite negative effect on the hybrid systems, and when noticing a low 12 volt a hybrid owner should dial up checking it's health and dialing in any one cars healthy usage range.