12 volt battery failing to start the car

Perhaps my earlier comment that the Prime should have fewer problems with this is incorrect, though it makes sense in theory. It seems that both owners who have had issues and posted to this other thread ( @WayneZ and @CruisnGrrl ) have Primes.

My 2023 Prius surprisingly wouldn't start today. | PriusChat

Now I'm wondering if this is a Prime only issue or are any non-Prime Gen 5 owners also having problems.

@Hammersmith also mentioned the voltage drain of a GPS linked anti-theft lo-jack system as a potential culprit. Apparently some dealers used to add them but now Toyota has made them standard equipment.

 

Don't confuse a poorly designed and poorly installed anti-theft/dealer repo system to what Toyota has installed for anti-theft. They are two entirely different things. The Toyota system will be integrated with the rest of the electronics and be able to go into a very low-power sleep mode until pinged by Toyota's servers.

My personal viewpoint on this lies far closer to JDS4's than anyone else on the thread. I don't believe this is an issue at all aside from user error or the extremely rare software design flaw(2020 RAV4). I don't even completely believe 23PriLE's situation. I'm wondering if the low voltage readings they've gotten aren't something of an illusion. Basically, I'm wondering exactly how the voltage is being read. They say they're using a voltmeter plugged into an internal 12V port(cigarette lighter style). Well, that might not be the same as reading directly from the 12V battery. Maybe that 12V port is at the end of a bunch of electronics that are pulling or restricting voltage. The battery could easily be at 12V+ even though a lower voltage is being registered at the port. As a 14+ year owner of Priuses, I have serious doubts about the "problem".

 

As I said I haven't had a problem with my car not starting but at least some of the accounts I've read seem to indicate that there is some issue. I suspect it's not widespread but I also don't think it's "a myth".

Most owners certainly don't seem to be having issues. In fact I've read some comments by owners of older hybrids saying that their 12 batteries lasted an unusually long time before replacement was necessary. Yet others say they've had problems. So it's a bit of a mystery and, being new to hybrids, I've been concerned / interested enough that I wanted to monitor the situation. Many of the posts that turn up in searches go back many years, though, so I'm more interested in Gen5 owner experiences.

For example, in the other thread @WayneZ said "This time the 12V battery ran out of power, it happened during short parking periods of no more than two hours. I was in the car but didn't use any other electrical devices. Before this drives, I had just fully charged the main power battery. . . . Fortunately, after jump-starting the car, this issue hasn't recurred in the past week."

I'm hoping he will give us an update and let us know if he's learned about any suspected cause.

Also in that thread, @CruisnGrrl just posted today that "Brought the car in for service. drove over 200 km after, today I got in the car to change some settings . . . and the 12v ended up draining in a couple minutes and the car wouldn't start."

That doesn't sound like user error to me. One day after driving 200km (120 miles) and the 12v battery ran down after a few minutes? Again, both of these were Primes so I'm wondering if that's a clue.

As for my voltage readings . . . When reading about battery issues here I found one comment from a few years back which said anything in the 11v range might cause problems. The poster didn't mention where the reading was taken but I decided to monitor the voltage myself and the lighter socket is the only convenient method.

I did wonder about its accuracy. I also have a high quality multimeter since I'm into home stereo gear that uses vacuum tubes. The plug in only measures to 1/10v. On one reading at the lighter socket the plug in meter measured 11.9v and I got 11.93v on my multimeter. So it's accurate enough.

There is obviously some current draw when measuring at the lighter socket because there is only voltage there when the car is in Accessory mode or the Hybrid system is on. I push the start button without my foot on the brake to go into ACC mode which, as I understand it, means most of the systems powered by the 12 battery are on.

I figure that's the voltage that counts because those systems need to be powered up before the car will go into Ready mode and they are likely seeing the same voltage.

I did find a difference between the lighter socket and the battery terminals. The reading there was about 0.4 to 0.5v higher, which would indicate that the battery had significantly more charge - maybe around 70% which should be fine. Still, I was surprised that it took ~11 hours for the battery to indicate full charge when using an AC powered 2A charger.

 

My 2020 Prime was at 11.2 volts at the battery a couple days ago. I drive it every day for about 8 miles total, and charge the main battery usually 1.5 hours every other day or so, depending if I go somewhere further. Car still started up. My first Prime did about the same maybe a little less. So I charged the 12 volt and left it charging all night. It took hours to charge at 4 amps. That’s it, the way it is for me, and I have to deal with it.

 

Here's the chart I saw posted. As you can see 11.31v represents a battery that's only at 10% with 10.5v being 0%.



What % is your traction battery after charging only 1.5 hours every other day? Is there some reason why you don't keep it on the charger overnight?

I'm totally unfamiliar with Primes but it would seem that leaving it on the charger for a longer time would result in the 12v being charged at a higher level but maybe that's not the case. Maybe you're just not concerned since it still starts but I've read comments that allowing it to go that low reduces the life of the battery unless it's something called a "deep cycle" battery which is designed to be dormant for long periods of time.

 

My charging is not done at home, it’s regularly done in a public area and usually 1.5 hours, 30% charge added appx. Car doesn’t charge the 12 volt fast enough for the drain, so I add charge to the 12 v. Did this on gen 2 also, but less. It is what it is. I am very concerned about life of the 12 v that’s why I charge it. This time I let it go longer before checking. Scanner will check it too. Eventually will have the desire to use the clamp meter more
to eliminate guessing. I initially made a reading but forgot what it was.

 

you can also leave the car in ready if you have a safe place

 

I left my almost-three-year-old 2021 Prius Prime Limited with active Toyota Connected Services undriven in hot weather for almost seven weeks, and I had no issues with the 12-V battery.

The reason why some drivers experience 12-V battery problems is that they don't realize that they shouldn't sit in the car unless it is in the READY mode, and they cannot only do short trips. Leaving the charging cable connected could be an issue, too.

 

Can you be more specific as to why this is an issue?
I go sit in my car for awhile every day after my walk for 15-20 minutes, and sometimes later just to get away from other people and have some silence for awhile. I don't turn on the car - sometimes I'll put down the windows but I turn it off again. I've done this for years and my Gen2 never seemed to have a problem with the 12v.

After reading your statement, I decided to turn the car on today. The first time the engine cycled on and off because I had the fan blowing. I'd turned the headlights off and the screen brightness down. The second time I turned the fan off and the headlights were on (I'd turned them back to auto earlier and forgot to turn them off). This time the engine never cycled, the entire car was silent for the 20 mins I sat there. As I went to get out I thought- "how is this better?"
The HUD and infotainment screens are lit up and the headlights are on. Isn't all that draining the 12v?

Please clarify how having the car turned on in Ready mode is better than getting in the car and just sitting there. I understand the car is waiting for you to start it up - but surely that's using less power than me turning it on and having all that stuff going without the engine cycling.

While not empirical at all - my personal experience is that both times my Gen2 hybrid battery failed it was within days after I sat it in for 30 mins or so with the A/C running and the engine cycling on and off during August in Florida. I work 11 miles (half highway) from home, so surely there was plenty of time for the battery to cycle between me doing that and it failing. Could possibly be a coincidence - we'll never know for sure. But it sure did turn me off to sitting still with the car running for a long period - after that I would get anxious about the hybrid battery just sitting in traffic too long.

How many miles do you consider a "short trip" to be?

For someone living in Nebraska a 'short trip to the store' might be 20 miles. For someone in a densely populated city a short trip could be 2 miles.

 

sitting in the car with it off isn't an issue.

turning it on creates a large drain on the 12 volt. eventually, it will die, or warn you to put it in ready.

putting it in ready bypasses the 12v so to speak, as the hybrid battery keeps it charged through the inverter, and the engine runs as necessary to charge the hybrid battery.

constant draining of the little 12v shortens it's lifespan.

you can't define a short trip. the car needs enough time in ready to recharge the 12 volt battery because there is a constant drain when it is off.
you would have to check voltage daily to see if you are driving enough

 

That’s somewhat true about trips, and so they charge the 12 v. like I have to.
The charging cable turns off the evse switch after charging is done. No connection, disconnected. I haven’t seen it go back on by itself until the handle is removed and replaced. Maybe it does, don’t think so. I mean, we all know about charging timing and the handle is plugged in a long time.
Very few Prius drivers don’t know about being in ready mode I would guess.
Someone needs to post the numbers going in and out. It’s like no topic to go back and forth about. Anecdotes versus anecdotes.

 

isn't there something in the o/m about not leaving it plugged in for more than 3 days?

 

Another owner @GGD just mentioned battery issues in this thread:

Services canceled and car removed from app | Page 2 | PriusChat

Their battery died 3 times and was replaced under warranty.

 

Defective batteries do occur. The HHR's original 12V was replaced under warranty for a bad cell.

 

I will look for it . When my car finishes charging the evse makes a click like a switch. Replacing the handle again doesn’t turn the evse back on. No connection is made. When the evse turns on power to the car there is also the audible switch click and the charging light turns on.

 

Wait a minute,
You're saying there is no way to leave this car while away on a ~2 week Vaca? It will drain and kill the little 12V battery if parked for too long?
You're saying that plugged in the car doesn't top up the 12V battery also?
It's only online with the DC to DC converter while powered up in ready mode?

Again, someone should read the "Owner's Manual".

 

Wait a minute,
Are you saying you can't go on a 'few week' vaca without killing the 12V battery? They go bad quickly if left in the discharged state.
Is this were 'New owners' are 'Doing it wrong'?
Are you expected to hire a 'Car babysitter' while away?

And most importantly, is this clearly stated in the Owner's Manual?

 

The thing about 3 days refers to battery heating in cold weather. While plugged in, the car will keep the battery above a certain temp for up to three days before that system shuts itself off. The time limit can be changed by a dealership to about a month, but that's only recommended for extremely cold conditions where the car might not otherwise be able to start(-20F and below).

(The first half of that comes straight from the manual; the second half by a poster on here that sounded like they knew what they were talking about - I haven't double-checked it.)

 

i'm not following your train of thought, can you clarify the questions?

 

Basically, does the Prime have an issue with be left, unplugged, unloved for 'a few weeks'?

Not that I want one, but a friend is considering one.