Okay. Who HASN'T had a 12V battery issue with their 2023-24 Prime?

Yes, it will. The drain on the battery when you bring the key fob within a few feet is quite large. This is even mentioned in the repair manual in the 12-V-battery-drain troubleshooting section, which is many pages long.

However, if the key fob is more than ten feet away, it is safe, and there will not be a drain. You can easily see at what range the large drain starts if you have a Bluetooth battery monitor. The battery voltage will suddenly drop by about half a volt or more when the key fob gets in the range, activating the systems and causing a current drain.

 

It doesn’t get much action on weekends.

I mean my mileage is just over 10000 and I’ve had the car since mid-late August 2023.

 

After posting earlier in this thread that I was doing fine, the battery died and had to get a jump start from road services last Monday. I can only attribute it to the cold weather, but compared to other parts of the country at the time it wasn't that cold in New Jersey (daytime highs in the low 20s going into single digits in the evening) when the battery died. I took it to the dealer on Saturday for checking and they said the battery was ok.

 

And no explanation why you couldn't start it? Maybe check for yourself:

Start up/No Start up? | PriusChat

 

@MyPriusMarvin

It is not the cold weather. It is the miserly BMS that likes to keep the 12-V-battery SOC low and doesn’t charge aggressively when you drive the car, as I have been explaining.

You must buy and hook up a battery maintainer at this point to save your battery. The BMS will never be able to rehabilitate and fully recharge the battery on its own after a full discharge. Get the Noco Genius or a similar smart battery maintainer and keep it hooked up for 48 hours without the car being driven to fully recharge the battery. (The last stage of the charging process with the Noco Genius takes 40 hours or longer.) Also, hook up the battery maintainer every other month to reduce/prevent sulfation by fully recharging the battery, as the BMS keeps the SOC at around 75–80% (if you are lucky).

 

Is the last stage of the Noco charging process the optimization, when the 25 to 75% bars and lit, and the 100% green is flashing?

Been driving a Gen5 for a few months now, and was checking the 12V voltage religiously at first, but it seemed to be okay with 2-3 weekly usage and charging. Weather has been below freezing overnight, and went to check the battery this AM, and it read 11.84V (using a multimeter). That's around 20-30% charge remaining?

Charged the traction battery for 5-6 hours (which I assume charges the 12V to some degree), and now have a Noco genius 2 attached. Within 30 min it went to straight to the optimization stage. I was expecting only the 50% or 75% bars to be lit.

 

The 12V system is powered by the grid when the EVSE is actively providing power to the car; charging, cabin preconditioning, or battery heating. There is some evidence it will charge a low 12V battery.

 

I attached my maintainer to the 12V in the trunk. I just routed the power cord out of the hatch area and let the hatch door close but the LED hatch light didn't go off until I really pushed the hatch closed.
Is there a best way to route the power cable of the maintainer outside of the car without squashing the weather stripping etc.?
I want all doors, hood and hatch locked during the charging process.
J

 

2024 Prime left in airport parking for about 3 1/2 days. Wife comes out and car won't start - battery dead. 9:30 at night and snowing. Gotta drive into town and start it for her - she can't operate the jumper confidently. She shouldn't have to. New car, nearly 40k, and this crap is happening. Can't use the full functionality of the app. because, you know, that drains the 12v battery. Can't leave it plugged in overnight because, you know, that drains the battery too. And of course, I can't have the app. notify me when the battery is charged because, you know, the app. will drain the battery (gotta love the irony here). I gotta put it on a tender every few days because, you know, who knows when it won't start. It is joke to call it "prime" as it certainly is not ready for prime time.

 

Chances are that the 12-V battery had a low SOC from the get–go (since you purchased the car). As I said repeatedly here, the BMS is not capable of bringing the battery to a healthy SOC once it falls below a certain value. Perhaps it is because of a bug in the complicated BMS algorithm—I don't know.

I think a good approach is to connect a battery maintainer for a couple of days immediately after you purchase the car. After that, depending on how often the car is driven, you might want to connect it every few months or so. Definitely connect it if the car hasn't been driven for over a week. And definitely connect it now, as you had a full drain. Other than that, you don't need to connect it everyday or every week.

 

That's a pretty much dead battery. You could get it tested with an electronic load tester (or DIY, such testers are avaiable for $50~100) for CCA. A lot of automotive retailers, in particular those selling batteries, will test for free.

Some here argue that since Prius doesn't use a conventional starter CCA is irrelevant; my 2 cents is that it's still an important barometer of a battery's "health".

I'm using a Solar BA5 tester, current itteration is BA9, they're relatively cheap. Ancel, TOPDON and others are popular.

Your current battery situation aside, you can check the car's parasitic draw, by putting an ammeter in series, between neg battery post and ground. Your current multimeter likely can do this, if it's got amps and milliamps. If it's not multi-ranging start with amps scale, just in case. You want to do the readings when the car's sat, at least 20 minutes, fobs well away, all doors shut. Basically disconnect neg post from ground, and run leads from the neg post and ground out, to your meter.

If you want to avoid the car losing memories, consider using a memory saver device, till all the connections to your meter have been made. And keep in mind, ONLY measure the back bround current, don't wake up the car in any way, say opening a door or whatever.

Normal phantom draw should be around 20 milliamperes. If you've got 50~100, or more, that's a problem.

 

Quick question, is this only a prime issue? Thank you

 

Definitely not. Any car that draws power from the 12v battery can be affected. A big abuser is the Telematics systems which is never really “off’. Personally I switched to a conventional Prius and have a ‘21 Toyota Venza. Both need special care to prevent 12v depletion.
I wonder what dealers do with cars on the lot for weeks/month prior to sail. I know the car I was looking at needed a jump to test drive. I know the battery is hosed and needed major desulfation(?).

 

@Prodigyplace posted a Toyota document recently, detailing what they expect dealerships to do. Main thing was disconnection of the negative cable.

 

I believe they are supposed to charge up the 12V battery monthly too.

 

No, discharged but not dead. The Noco Genius will easily bring it to full charge. There shouldn't be more than about 10% capacity loss.

 

No, Gen 4 and Gen 5 Prius HEV and Prius PHEV all have the same miserly battery-management system (BMS), which sometimes fails to bring the SOC to a healthy level. The remedy is to occasionally use a battery maintainer like Noco Genius. In fact, you should hook up the battery to a battery maintainer for 48 hours as soon as you purchase the car to bring the SOC to 100%. This should be the most important item in the Prius new-car checklist.

 

They don’t do anything. That disconnection mentioned in that document is not for the entire battery but some fuse for some nonessential accessories.

 

I'm just thinking of our experience, with the 2010 (build date Aug 09) we bought in November of 2010). We found it wandering their lot, in a storage shed, sheltered, but coated with apparently undisturbed dust, dead bird lying beside it.

A day or two later, when they'd dug it out and washed it, for us to have a test drive, they "had it running to warm it up". That ruse came apart after the test drive, as we were signing the agreement of sale paperwork: had to go back out and check the kms on the odo (about 10~15), and the car wouldn't boot, dead-as-a-doornail. We added 12 volt battery replacement as a condition of sale.

That's Open Road Toyota in Port Moody.

 

That Noco Genius charging profile sounds right. The first stages take only a few minutes, but the last stage takes about 48 hours until the green LED stops blinking and becomes solid. So, you need to leave the Noco Genius connected for 48 hours if you want to reach a truly 100% SOC. The link below shows how the Noco Genius charging profile looks like. Leave the Noco Genius connected until the green LED becomes solid (up to 48 hours) if you don't need to drive the car so that the battery will be fully optimized with the maximum safe charge possible.

AGM battery for Gen 4/Gen 5 Prius/Prius Prime and observations on the 12-V charging system | Page 12 | PriusChat