12 volt battery failing to start the car

You must have missed my post where I posted an excerpt from the owner's manual.

●When the vehicle is left with the
AC charging cable connected, the
electricity consumption amount of
the 12-volt battery increases due
to controls, such as the system
checking, operating. When the AC
charging cable is not needed,
remove it from the vehicle.

The AC-charging cable must be disconnected when charging is complete; otherwise, it will drain the 12-V battery as the owner's manual explains.

How are you going to plug in a cable to heat/cool the lithium-ion battery if you park on the street or in a parking lot if some OEM had provided such a feature?

 

You haven't thoroughly read pages 108-110 of the manual. There's some ambiguity as to whether the standard battery heating function is continuous with the AC cord attached, but there's no ambiguity about the Alaska/Canada battery heating function. While the cord is attached, the car will use the traction battery to power the warming system to keep the battery above a certain temp. Once the traction battery is depleted to a certain point, charging will automatically resume to recharge it. This system will continue to cycle for up to 31 days before turning itself off. It does not say exactly what temps trigger the system to operate, but another source said the car might not be able to start below -20(I don't know if F or C), so it's likely something above that.

As for the standard battery heating function(non Alaska/Canada), it could be read that it only functions to prep the battery for charging, or it could be read that it does the same thing as the above system. What is clear is that it only operates for 3 days before shutting itself off.


I think this is a case where you're both right. Leaving the AC cord plugged in can indeed slowly drain your 12V. But leaving it plugged in can also keep your car at a safe operating temp in extremely cold climates. If you live in one of those climates, you just have to balance your needs and maybe install a trickle charger that's easy to plug in to keep your 12V batt topped off.

 

The 12 v drains with or without the cable attached. The question I have is how much more in amps does the 12 v drain with the cable versus no cable. Writing without numbers goes on forever. Have the number, all done, know what is going on.

 

In Southern California, I don't need to worry about battery heating.

That said, this feature only seems to be there to heat the battery before charging—not to heat it during storage. It is connected to scheduled charge. In fact, it stops for good after three days. Therefore, I don't see any point in leaving the cable plugged in for storage, hoping that it will heat the battery.

 

You can perhaps find out. Nevertheless, I don't need to, as Toyota recommends unplugging the cable when charging is finished to preserve the 12-V battery charge. Even a small amount of drain is too much drain for my purposes. I even changed the default auto-off setting for the lights so that they go off as soon as I open the door and do not drain the 12-V battery.

 

Confirmed via TIS that the battery management system continues to keep the battery above a target temp for up to three days if left plugged in and the option is enabled in the settings(31 days for Canada/Alaska).

The exception is if start-stop charging mode has been selected. In that case, it will warm up the HV battery so it's ready to be driven at the scheduled stop time. Once that time has passed, the heater will shut off and not reactivate. (does not apply in Canada/Alaska below certain temps)

TIS is also clear that the heating mode is so the car can run in EV mode from the very start of the drive and does not have to do with prepping the battery for charging.

 

Where/how in TIS?

Interestingly, according to NCF in TIS, battery starts charging regardless of how cold it is, which brings the usefulness of the battery heater into question.

 

Where did you come up with this theory?
I realize you are new to Li-ion batteries.
They have very little 'Self-Discharge' and when the power contactor is open there is no drain at all on the pack.
Also, Li-ion always have a 'Low Voltage Cut-Off'. The can't discharge to a bricked state, (well maybe in years of storage, possibly.)
And, if it somehow one got to the Low Volt Cut-Off' it would just need a bit of HV charging to get it back online.

What about when it gets above 100°F (and since the pack is in the cabin of the car it most likely is much hotter than ambient temps)?
Should you worry about Cooling the pack.

Again: What does the Prime have for TMS?
(I guess I could do my own research, but "Frankly my dear......")

A Li-ion pack should be in the happy temp range for charging ,and most importantly, while be driven.

All quality PHEV and BEV have a TMS to
Heat and Cool the pack as required.
Are you now questioning why any of the cars with Li-Ion batteries need a TMS?

 

I will eventually , but have no need to as I never leave the cable plugged in as I always am charging at free places. It’s just your words, “otherwise, it will drain the 12-V battery as the owner's manual explains.” The manual says more drain than disconnected, not all. How much more. My car drains the 12 v pretty fast all disconnected, and I have had two of the same year cars.

 

Li-ion cells below 0C will be damaged if charged at normal rates. The PiP charged at a very low rate until the pack got over that temperature. Everything else has some type of external heating.

So, how warm does the Prime's battery get from the heater alone? Can it get a pack at sub freezing temperatures to room temps, or just above the damage threshold, and let the charging process heat the battery up more?

 

Sorry, I could have been a little clearer. The battery is indeed warmed up prior to/during charging, but that's just part of the standard charging routine. There's also a specific 'battery heating' function in the settings that is solely to get/keep the battery up to temp so you have access to full torque from the HV battery immediately upon starting the car. Both systems use the same heating elements under the battery cells. I'd give exact temps for each function, but they weren't listed in the TIS section where those functions were described.

 

That's just above freezer settings to refrigerator levels.

 

New Car Features -> Engine / Hybrid System -> Hybrid Battery Control -> Plug-in Charge Control System -> Plug-in Charge Control

They even show graphs of the temps over time so there's no way to misinterpret how the system operates.

 

If your car is draining the 12-V battery fast with all disconnected, there is definitely something wrong. As I said, I left mine for over six weeks, which is a significant length of time, with no issues.

If the cable-plug-in drain weren't an issue, Toyota wouldn't explicitly mention it in the manual.

 

Actually, just refrigerator levels.

Home refrigerator/freezers should be set to 40F/5C or a little below for the fridge and 0F/-18C or lower for the freezer.
Sorry, food safety is a thing for me.

 

Yes, I have the NCF as I mentioned. I didn't notice the "31 days" you claimed, which is in the owner's manual but not in the NCF. I also pointed out that the battery starts charging regardless of the temperature.

They did improve the figures in the 2023 NCF by adding the control "hysteresis," but it is otherwise identical to the Gen 4 NCF.

 

Oops, got the F and C crossed for fridges there.

Was once involved in a shelf life project for hot dogs where one set was stored at 10C for weeks. It got unpleasant at times.

 

No, as I pointed, it is not. Look at the figures more carefully: The battery starts charging immediately regardless of the temperature, and there is no preheat before charging. Heating and charging start at the same time when the car is plugged in.