I want to alert everyone of an issue with the auxiliary 12 volts battery in the new Prius prime 2024

Perfect

 

I just had my third 12 volt battery installed and just clicked over 3500 miles… the original was tested as “bad” and the replacement battery was also tested as bad. Both had the same issue - took a charge but when tested under load they could not hold the charge in a normal fashion. Hopefully the 3rd time’s a charm but I now carry a battery charger in my new Prius which is a pretty unacceptable situation.

 

is it the batteries, or is it the car?

 

I don't anyone's tested a gen5 background amp draw yet.

There does seem to be a problem acknowledged by Toyota, if you leave the hybrid battery charger cord attached.

 

I can get an idea of parasitic drain when car is off with the battery monitor. Have seen a few tenths of a volt decline every night. That’s as far as I have taken it. I suggest this is more accurate than a multimeter spot check on drain while hood is up etc. Someone would have to have the desire to spend the time and effort on it.
My Toyota truck, it stays flat during a night, the Prius has a downward curve.
If a car was left off a few days it would be more data.

 

why hasn't everyone gotten the software update that supposedly fixes it?

 

toyota is not going to add a trickle charger because the hybrid battery is isolated from the rest of the car when off for safety reasons.
have you read through the other 12v threads to see how they solved the problem?

 

The problem isn't that the batteries are coming bad or defective from the factory. They are good when they come from the factory.

The problem is that Gen 4/Gen 5 Prius/Prius Prime have a very high drain on the battery when the car is off or not in the READY mode. It is especially high for Gen 5 and Prius Prime, Gen 5 Prius Prime having the highest drain. If the battery doesn't get fully charged when the car is driven (typically only for short trips), the battery state of charge will go low. If the battery stays at a low state of charge for an extended period of time, it will go bad and no longer hold its charge.

These are the only remedies:

• Do frequent long trips.
• Do not sit in the car unless the car is in the READY mode.
• Do not leave the headlights or radio on with the car not in the READY mode.
• Do not leave the AC traction-battery charger plugged in for longer than overnight.
• If the above fails despite sticking to all, do use a good battery maintainer.

 

Looking up the part number, I see no indication of it being lithium as you stated in Post #1, or of being anything other than an ordinary lead-acid battery.

 

Of course it is not lithium-ion (LFP type). A lithium-ion 12-V battery cannot be used with Gen 4/Gen 5 Prius/Prius Prime due to the presence of a battery sensor in the car and a battery management system (BMS) in the lithium-ion battery, which would conflict and likely result in the check-engine light coming on. Besides, you would get no benefit from a lithium-ion battery, as there is no 12-V fast charging.

That is the Toyota TrueStart group-size DIN H4 lead–acid battery. I hope it was center-vented so that the Gen 5 vent hose could be connected.

 

Not likely the original 12 volt discharges and is ruined when shipped from Japan. They disconnect the 12 volt by a fuse. It’s part of port prep to reconnect and recalibrate systems affected. The ruination must happen when dealers get their hands on them.

 

It'll take someone, disconnecting the neg cable, putting an ammeter in series, to figure out what's happening.

 

What is it and how do we get it?

 

The second the door is unlocked, hood opened, the one reading obtained won’t mean much of anything. If the hood is left open and readings monitored over a day at ten minute intervals would tell more. Then your car is no longer in the emissions ready state, all settings have reverted to default, so what that does to the readings no one has said. A battery monitor can show voltage drop over any time period, voltage spikes, all without touching the car. With voltage drop it can give an idea of parasitic draw. On my car every night between midnight and 1 am there is a significant, short, voltage drop spike. I would bet it is on all gen 4.

 

It's a gen 5 in question, with the battery in the hatch again. This is what I did on my Gen 3, I didn't encounter any problems, got milliamperes in around 20, with spikes every few seconds to about 40, possibly due to the security alert icon on the dash. It gives a direct reading of the at-rest amp draw:

1. Disconnect neg cable (at the body end is likely most expedient)
2. Connect two long wires, one to loose end of battery cable, the other to bare metal of the car body (connecting the latter using the removed neg cable bolt location is likely most expedient:
3. Run the two wires out over the hatch threshold and down to the slab, and tape them securely, comfortably separated.
4. Close all doors, and wait half an hour, with fobs well away.
5. Connect ammeter to the two wires, start in amps scale (just in case there's massive drain), then if nothing, switch to milliameres.

Doesn't account for something that occurs on a schedule, granted, but it's an accurate test.

 

Idk, but it is in one of the battery dying threads

 

I experienced this same exact scenario this morning! 2023 Prius Prime XSE…

Had it towed to the dealership where they charged up the battery with a “GR8” charger/tester. They said everything was fine now and to come pick up the car. I told them there is something wrong, but they insist the battery is ok.

In my opinion, this is a problem which will re-surface so I can’t trust the car. Told them to keep the car to see if it fails again.

 

(Re-post error)

 

Was phantom draw amount mentioned?