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

They are required by Toyota to test the battery as part of the PDS here in the US.

 

I think it is an issue for both versions of the Prius Gen 5. I've seen a few posts here by Hybrid only owners on the 12V issue.

 

My Prime has been on the 12 v charger all night. The car has been charging the battery well every day in the morning, since the temps went into forties overnight. Still the soc was 69% last evening after a short drive. It wasn’t charging during the drive. On the 12 volt charger it went. Part of my ownership now. The battery monitor makes it a fact driven process rather than guessing.
I haven’t checked into if a permanent 12 volt maintainer could be mounted under the hood. I would have to open the hood anyway and by now I am pretty quick about putting the clamps on and holding the hood up with my head to save the step of using the hood rod. I use a waterproof charger if it’s outside and wet.

 

I hope this does not also apply to my Gen 5 2025 Camry XLE.

 

It probably does. Toyota probably uses the same miserly, bug-ridden BMS algorithm in all of its new vehicles, especially the hybrids, in which they think they can squeeze an extra 0.1 mpg by limiting 12-V-battery charging.

 

After a night of charging, a 69% SOC makes no sense. As I told you, you shouldn't trust the SOC numbers shown by the battery monitor. They are calculated by a simple buggy algorithm using the battery voltage alone. There is no way you can calculate the SOC from the battery voltage alone without also monitoring the current. The best way of doing that would be to look at the resting voltage, but that’s not what the battery monitor does.

Also, there is no need to connect the battery maintainer everyday or even every week if the car is seeing half-hour trips a few times a week. Once every few months should be enough. The daily SOC loss is around 2.5%; so, if the car is not driven for longer than a week, the battery maintainer should be connected.

 

It was after driving a short trip in the evening in ev mode, no charging of the 12 volt. The soc is more or less ok, good enough for the purpose, regardless of what is said to the contrary. I look at monitor often and find no discrepancies that would indicate extreme oddball readings. Everything proceeds as expected when charging etc. I have the Ancel type on the Prius. I think there is more to it than you may know although it seems you know a lot. it would be like a cell phone or power tool battery soc readout I think. Do you question those? I read about it once but honestly it isn’t that important to remember. I think it works and it seems to be about right, however it works.