I've only had this 2024 Prius Prime SE (PHEV) for 18 months. The the car did a meltdown when I tried to start it recently on a cold morning (headlights, taillights, and dashlights all flashing intermittently and at different times.) I phoned the local Toyota Service. They said they couldn't look at it for THREE WEEKS! I looked at a few Youtubes to find out it's probably the 12 volt battery. Turns out that the 12V battery went right down to 4V! (No, there was no lights left on overnight). I charged it and took it to Toyota. They looked at it right away (that's another story). They charged it and said it 'tested' out to be in good condition! I said it must have internal damage. They said it wasn't driven long enough. I charged it last night. This morning it's down to 12.2V. Won't take long before it's below 11 volts, or lower as the days go on. We had a 2008 Prius before this one and didn't have this issue. Also, you could see the SOC of the 12V from the drivers seat. Looks to me that there is more of a parasitic drain on this generation, for the capacity of the battery. Anyone else have this problem?
I would be sceoptical. Any 12 volt battery drained to 4 volt will not last much longer, if at all. What's your parking situation? Do you have secure, off-street parking with 120 volt AC outlets available? If so,l look it smart chargers, around 5 amp rating, either on-board or exterior to the car, depending on the situation: if you're parking outside an onboard charger is more secure, just a power cord protruding from grill (like a block heater cord) is the usual setup. If you're in a secure garage you could also use an exterior-style charger. My setup:
The 12 volt battery discharge problem is common for the generation 5 prius. The problem has several causes including: The remote control too close to the vehicle for example when washing and/or waxing the vehicle or even in the garage during maintenance. Those who do not close the Toyota application after use. The fact that if the temperature is above zero Celsius, the DC-DC converter charges the 12 volt battery only 5 minutes after the vehicle leaves, after which it only maintains it. When you recharge the high voltage battery, it's the same, you only recharge the 12 volt battery for 5 minutes. In short, we discharge it more than we recharge it. On this document: Toyota/Lexus 12v Battery Failures - Analysis of Charging Issues - Deep Dive Analysis & Workaround by /u/andy_why - Google Docs It is recommended to disconnect the connector near the negative terminal of the battery so that the DC-DC converter always charges at 14.4 volts (not just 5 minutes). To find out the state of health of your 12 volt battery, test your SOH, if it is less than 75%, it should be replaced. The SOH gives the remaining capacity of your battery, for a 45 AH battery at 75% SOH, this means that there is only 34 AH of capacity remaining. It is easy to find and buy a tester that measures SOH, garages also have this tester. Using a smart charger is a good idea, but avoid NOCO where you stay, because it barely charges the battery to 60% when the temperature is below zero Celsius (poorly temperature compensated). The best smart chargers for very low temperatures are the BATTERY TENDER.
Didn't know that about the low temp performance of the NOCO. You live in a cold weather testing laboratory, so you should know!
You can charge the 12 volt by putting the car into “Ready” with a charged up Traction battery. Shutting off the heater will prevent the engine from running. I believe that you can lock the car with the manual key. Leave it for 4 to 6 hours. Unplugging the battery monitor at the negative terminal, as suggested by Danny Dan, will also help, but in cold weather the charge voltage should remain above 14 volts without doing so.
This all sounds very familiar. I have experienced many dead batteries, which happens at unpredictable times. I alerted the dealer to the problem, but they informed me that the factory battery was testing up to spec. Another dealer actually replaced the battery, to no improvement at all. I have my own theory; I believe the live updates are draining the battery at variable and unpredictable rates. Sometimes the 12V battery will hold a charge for a week, but other times, it drains in just a few hours. I believe this to be a design flaw, but since no update or recall is available, I have resolved myself to using a battery maintainer and a booster pack. This all could have been avoided if the system were designed to maintain the 12V battery off the hybrid battery.. We can only hope that Toyota will someday see the light and fix this problem.
I've had poor luck with "smart chargers." They tend to shut down if the battery isn't in top condition.
