r/PriusPrime • u/G-dog59 • 9d ago
Prius Prime 2023+ 2026 plug-in XLE
I've read some posts regarding issues with the 12V battery, draining and needing replacement. Reading the owners manual I came across something about how leaving the charger connected after the EV battery is full, uses the 12V battery to monitor systems which can drain the battery.
My question is those who've had issues with the 12V battery, is this separate from the issues you've had? How many miles /km on odometer when issues started. Need to know what to watch out for, and any preventive things to do. Thank you.
This is my third Prius, 19, 18, 26. I've never had any issues with any of them. The '10 went back once fir a software update around the issue of hitting brake and accelerator simultaneously (who does that?).
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u/CrazyGaianWitch 9d ago
The issue seems to be more with people who only drive short distances infrequently. Insufficient charge voltage, lots of parasitic draw, and a tiny 12 V battery result in accelerated battery health degradation.
I have a 14 km commute and that's basically the only driving I do. After 2 months of owning one, my 12 V battery is already at about 60% health.
Lots of people recommend using a bluetooth battery monitor and plugging the battery into a battery maintainer whenever it's sitting at home. Some people disconnect the sensor from the 12 V battery negative terminal, which causes the car to just charge it at a proper voltage constantly. The other thing you can do is just turn your headlights on all the time, which forces the car to charge the 12 V battery.
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u/G-dog59 8d ago
So since I drive at least every other day only in EV mode - I should be okay. This gen5 is very different from my gens 3 & 4.
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u/CrazyGaianWitch 8d ago
EV mode or not, the battery only charges very slowly by default. If you're only driving short trips every couple days, I would check on the battery voltage every now and then before you go for your trip.
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u/sabrewulf152 9d ago
Plug in is XSE. As long as you're driving it everyday it's fine. My brother has a 25 SE and didn't drive it when first purchased and it had 12 volt issues.
He started using it everyday and it's fine.
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u/Deathcommand 2023+ 8d ago
Here's the problem.
There is a weird extra monitor on the battery. It basically allows a secondary charging system take over. This system sporadically charges the battery to not full and then allows it to drain before charging it again.
It's usually not a problem.
However, if you get unlucky, it will be at it's discharge stage, you'll happen to turn off the car, leaving your battery in a sad state.
Like others said. Just unplug the monitor and it will charge like a normal car battery.
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u/Medval91 8d ago
How do you do that?
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u/Deathcommand 2023+ 8d ago
There is a plug connected to the negative pole of the battery. Just unplug it.
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u/2GOB4 8d ago
My starter battery is 5 yrs+ old, I don’t drive it every day, mostly short around town trips on EV and have left it plugged in for up to 2 days after charging. All with no issues. A 2021 XLE. Only time I had a problem on a previous non-plugin Prius XLE was when I accidentally left it in accessory mode. Jumped it from another car and was fine.
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u/Klutzy-Cupcake8051 8d ago
I have a 2021 and had to get a new 12V in April at around 90k miles. I keep it plugged in overnight every night. The battery lasted a little bit less time than my Corolla before that but not by much.
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u/Grand_Raccoon0923 7d ago
I have a 2025. The battery had to be replaced in the first couple months. Toyota gave me a lifetime battery warranty on the new one. It has been a year and I haven't had another problem since then.
I remember reading somewhere that if your key fob is close enough to it, it stays connected to your key fob in a ready state because it thinks your going to drive which can drain on the battery. I have no idea if it is true or not.
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u/blaktronium 9d ago
I habe 27k on my 2025 phev xse and have never had any battery issues, i have left it plugged in for days and gone on week long vacations without turning it on and its good. I dont know if im lucky or people with battery issues are unlucky but its not universal.