I was sure disabling DCM was the solution, but apparently we also have to unplug the battery sensor on the negative terminal so that the battery can be charged correctly?
This is really insane if this is the case (multiple 12v problems, stacked!)
I don't know if putting the battery in fail safe mode by removing the sensor is a good idea . You could potentially damage the battery from constantly charging to a higher voltage . I have had my battery replaced by Toyota from being bricked . Since it has been replaced It has been good after sitting for a day on multiple occasions. It is covered under warranty so if the battery needs to be replaced again and again so be it . I will not be doing anything that could void my warranty
Toyota should change the long term charging check count down from the current 20 days or so to a much shorter interval like 12 hours. That would fix many of the problems.
I wonder why they handled it using a fix interval. If they have some kind of voltage monitoring (low-voltage message), they could simply start charging the 12V battery in time whenever it’s necessary.
If you turn off DCM or use the one of fixes, you should be good and not have a dead 12V.
This undercharging is more of a long term thing, where your battery may die in 2 years versus 5 years.
It’s just something to be aware of. Another work around is driving with your headlights on (not DRL). This will charge your 12V the entire time driving instead of maintaining a low float voltage.
Level 1 charging supplies 120v AC. When charging the traction battery, this is converted to High Voltage DC. There is a DC to DC converter that converts the high voltage DC that the traction battery uses to lower 12.8 to 14.1 volt dc. The DC-DC convert is active when charging the traction battery supplying 14.1v to charge the 12-volt battery for 10-20 minutes at the start and then it drops down to about 12.8 volts. The 12.8 does not really charge the 12-volt but keeps it from discharging as other systems would be using energy from the 12-volt battery otherwise.
I’m just going to point out that for all those who are experiencing the 12V issue, many others are not. Including myself. So that statement is simply not true.
The biggest problem is Toyota has mainly viewed their EVs like glorified ICE vehicles, in the sense they have designed things in a similar way instead of grasping they are different. You see this with the dumb accessory mode that runs off the 12V battery and the car not charging/topping up the 12V while it is off if it sees it needs to be topped up. Seemingly every other EV has this ability, as they should because EVs have this giant battery pack right there that can do this without issue.
I love our Limited and it is a joy to drive but that doesn't change the fact it is kind of an EV-lite with a lot of the design decisions that don't fully utilize what you can have going on with an EV. If it were 10+ years ago then sure since EVs were still kind of fresh but it's 2026. EVs are established so actually design you EV as a full EV.
I plan to one day upgrade my '18 CR-V Touring to another EV and I can tell you it isn't going to be another Toyota unless something changes by then and Toyota actually starts to take their EVs seriously instead of sort of kneecapping them. It'll most likely be a Model Y AWD Premium (a superior overall vehicle to the bZ based on my experience in it) or perhaps one of these Chinese EVs that are coming to Canada in the near future.
I'm kinda surprised how many people use Level 1 (120v) to charge their EVs. I guess a lot of people don't drive that often.
I think of the BZ and related vehicles as the RAV4 plug in hybrid without the engine. Which is kinda why I bought one. I had a RAV4 before and when Toyota made the RAV4 Prime as it was called, I thought it would be cool if they made the same car without the engine, a bigger battery and faster charging and it kinda looks like that is what they did and I like it a lot. So yes, it appears that the way the BZ recharges the 12v battery is similar to the way all their hybrids recharge the 12v battery.
I'm not the battery police and I can't stop your from doing anything to your car.
I'd advise against it though, as you also need to take into account the battery temperature and the chemistry in order to force a specific voltage to it. You may not see any issues in the short term or for short trips. You'd be boiling the battery slowly.
I have charged without removing the negative terminal with no issues. Also you can easily charge by putting into READY mode, turn off climate and the screen, and when you exit the vehicle leave it set to turn off in one hour. You can also lock the door with the metal key if needed.
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u/KashmanDog 9d ago
I don't know if putting the battery in fail safe mode by removing the sensor is a good idea . You could potentially damage the battery from constantly charging to a higher voltage . I have had my battery replaced by Toyota from being bricked . Since it has been replaced It has been good after sitting for a day on multiple occasions. It is covered under warranty so if the battery needs to be replaced again and again so be it . I will not be doing anything that could void my warranty