Third day with new car, dead 12V battery, second day in a row :(

Just had the exact symptoms..,,,,,waiting for a fix! Hopefully just a dud battery.

 

Plugged in my prime overnight for the first time yesterday, have always just charged it during the day for the amount of time it needs for a full charge before unplugging it. The car started fine this morning but midday I went to sit in the car for 5 minutes with the ignition in the accessory position and the the car gave me a low battery warning. Thankfully the car still started later in the day.

According to a thread on the prius prime subreddit it appears that whenever the car is plugged in and charging, it's pulling power from the 12V battery without charging it, causing the 12V battery to be run down.

 

Possible to leave the car on while it is plugged in for charging?

 

While the car is actively charging, the 12V system is getting power. When not charging and plugged in, the system draws power from the 12V battery to monitor things. I would not expect it to drain the battery that much from one over night session. The low battery warning can be very cautious, too.

The battery or drained some, or bad, before hand. It is also a small battery, as it doesn't need to be powerful enough to turn over an engine. Just being in Accessory mode could be enough to drain it to the point of the warning light coming on.

 

Sitting in the car with the ignition to accessory even for a few minutes is a receipe for disaster, It has been often documented on PC chat.
You should always turn the car READY not accessory , because when the car is READY , the traction battery provides power to the 12V battery thru it 's DC to DC converter keeping it charged . Using accessory doest not , so it will discharge rapidely because all the ECU and computers are on and consuming a good amount of energy.
As for charging when the car is plugged and charging, the 12V battery does get charged thru the DC to DC converter

 

Toyota uses three terms for how "turned on" a car is:

1. Accessory (one push of of Start/Stop button, without foot on brake): this mode basically allows you to listen to the radio.

2. On (two pushes of Start/Stop button, without foot on brake): this mode has most systems on, except the engine won't run.

3. Ready (one push of Start/Stop button, with foot on brake): car is fully on, engine will cycle on/off.

For just sitting in the car, say listening to the radio, #3 (Ready) is the only way to avoid drawing down the battery. That's not to say in Accesory or On, you're going to kill your battery in a few minutes, but they are best avoided.

 

Thanks for your clarification , I edited my post #26 after reading yours , READY is the only safe choice and noting that Tooly has a prime, the engine will not start because the prime defaults to EV mode when on Ready

 

Hmm, must be a Toyota Prius thing with the Acc on? All I was doing was listening to the radio. On my previous 2 VW's I could sit for an hour with the car in the Acc position and just listen to the radio with no ill effects. This was with the original 5 year old factory batteries. Heck even my 2021 4Runner I can do the same with no ill effects.

I wish I could link to the reddit thread but the forum here does some weird formatting on the link. Any way around that?

 

Ah ah !,your 2 previous VW and probably your 4Runner had a starter motor , hense a big 12V battery to crank the ICE motor , in the Prius there is no starter motor , when the ICE of the prius needs to be started,it is the TRACTION battery that feeds the MG 1 to spin the motor not the 12V battery. SO if you only listen to the radio put the car in READY ......because it's not only the radio but all the computers and ECU that are sucking power...and the 12Volts battery is much smaller in capacity.....and Yes the Prius is a different animal..no torque converter , no alternator , no classic transmission

 

Theres no free lunch; if you’re listening to the radio you’re using (and not replenishing) the 12 volt battery. With a smaller battery that use has more impact.

 

I was warned to turn the Outback on before going through the settings menus. There is more drawing on the battery these days. The SKS system may have been pinging your fob the entire time for instance. Then in a full hybrid, the starter battery just needs to boot up the computer and flip the relay to the traction battery. It is sized accordingly.

 

Yep ,some old habits have to be abandonned .....like using the accessory mode....or worse trying to boost a dead battery on an ICE car from a Prius car .....

 

Ha ha, no way, the Gen 4 plug-in blows the Gen3 plug-in away.

 

you're taking me out of context (intentionally?) we were talking about 12 volt batteries.

and a second way the pip was better was the hatch floor height

 

Thanks for the tips guys, still wrapping my head around PHEV vehicle as I've only every driven ICE vehicles.

This is the link to the reddit thread, it's an interesting read and for the original poster, Toyota seems to be at a loss as to what the issue it with his car.

reddit.com/r/PriusPrime/comments/14pqpwk/2023_prius_prime_drains_12v_battery_when_plugged/

 

Not in my experience. I have been having no issues with the 12-V battery whatsoever. I think the issues are caused by unintentional driver abuse—probably sitting in the car with the car not in the ready mode, doing only short trips, etc.

New prius Prime with dead 12v battery this morning | Page 6 | PriusChat

Yes, bigger PHEV battery in Gen 4 = higher trunk deck.

 

there are a bunch of prime 12v battery threads, no pip 12v battery threads. your experience is one, but there are many others, and it has nothing to do with user error

 

That was an engineering fail.

 

Is it because there are no PIPs other than yours?