12 volt battery failing to start the car

I am repeating what Toyota said in the manual. As I said, mine had no measurable discharge when I left it for over six weeks.

There is a battery heater in Prius Prime, and the A/C is used as a battery cooler.

 

No, it has not. Gen 5's thermal-management system is identical to Gen 4's. I have the Gen 4 NCF.

Hardly anything changed from Gen 4 to Gen 5 other than the PHEV-battery capacity. They did add a new "my-room mode" feature, in which you can run the A/C etc. from the AC-charging cable, though.

 

Oh my god.

Do you think the battery management system is going to try to charge the battery at full rate if doing so will damage the battery because it's super cold(like -40?)? No, it's going to warm the battery up to a safe level before putting the spurs to the charging. Maybe it will start charging the battery at a very slow rate while it's also heating up the battery, so it might not be pre-heating by the strictest definition, but that's splitting stupid levels of hairs. The main portion of the charging cycle will not start until the battery is up to a safe temp. That's the point I was trying to make.

Will this happen to you in SoCal? Of course not. But not everybody lives in SoCal.


The points I'm trying to make for those who are not already versed in the intricacies of gen5 Prime charging:

Should you leave the charging cable plugged in for extended periods when charging isn't needed?
- Generally no.

Why?
- Leaving the charging cable plugged in adds increased draw on the 12V battery, depleting it faster.

How much faster?
- We don't know. But it's still best to not have it plugged in for multiple days in most cases.

Most cases? Does that mean there are some cases where you should leave the charging cable plugged in if possible?
- Yes.

What are those cases?
- When it will be below 32F/0C when you start driving.

Why is that important?
- Because the BMS won't allow the car to draw full power from the battery until it's at a safe temp.

Is that all?
- No. To get the battery up to a safe temp as quickly as possible while driving, the BMS will use power from the battery to operate the heating elements(shortening EV range) as well as running the ICE(using fuel).

So how will leaving the charging cable plugged in prevent this?
- If the charging cable is plugged in and the battery drops below the safe temp(around 32F-36F/0C-2C), the BMS will use power from the battery to run the battery heating elements. If the battery drops below a certain state of charge, the charging will restart to top the battery off.

How long will this process go on?
- In most cases, this cycle will continue for up to three days before the BMS cancels it.

This sounds like it might waste power by keeping the battery warm when I don't need it to be. Are there any options for me to only have the battery be warmed right before I leave in the morning?
- Yes. If you use the start-stop schedule option for charging, the BMS will not maintain the battery temp after charging is complete, but it will still warm up the battery again so it's ready at the scheduled stop time.

Are there any drawbacks to using this method?
- Yes. If you end up not leaving at the scheduled time, the battery will eventually drop below the safe temp, causing reduced EV range, increased ICE use, and reduced EV power at the start of your drive(until the battery is warmed up).

Is there anything else about leaving the charging cable plugged in that I should know about?
- If you happen to live in an area of extreme cold where the temps drop below -20F/-30C, there is a chance the car will be unable to start its systems because the HV battery gets too cold. This chance increases as the temp falls. For these regions, the BMS will maintain the battery at a safe temp while plugged in for up to 31 days regardless of which scheduling option was chosen.

What regions have this option?
- In North America, cars sold in Alaska and Canada have this option by default. People living in other cold areas(say northern Great Plains), or people planning to travel/move to those regions, can have this option turned on at a dealership.

 

Your rant is totally off the rails. Why are you writing all this?

I only pointed out that there was no preheating, which you claimed to be there. Do not be offended for having your mistakes corrected. It was not splitting hairs—it was gross misinformation on your part.

Of course a cold battery should not be charged fast. By the way, if you know that much, you should also know that it is not even possible to charge a cold battery fast because of reduced diffusion rate at lower temperatures.

And, @Trollbait, I am calling you out for liking obscenity.

 

There is preheating. If the car started charging as soon as it was plugged in when the battery is at freezing temps, there would be permanent damage done to it.

 

As the NCF shows, heating and charging start at the same time. Of course, as it was pointed out, the charging rate (C rate) at lower temperatures will be lower.

You can research it, but I believe your statement about permanent battery damage is not accurate or even correct.

While it is not best to charge a battery at freezing temperatures, I doubt it would cause permanent damage, especially with reduced C rates. I saw an inaccurate post of yours on the same subject in a related thread where you Googled a statement that lithium-metal plating on the anode surface occurred if the battery was charged at low temperatures. This statement is not accurate either. Do not believe everything you read on the Internet. Lithium-metal plating only occurs if the diffusion rate of lithium ions in the anode cannot keep up with the charge rate (C rate), and for low C rates, this shouldn't be a problem even at lower temperatures.

 

Speaking of C rates, they are not high for Prius Prime to begin with: less than 0.5C (longer than 2-hour 0–100% charging) for Gen 4 and less than 0.25C (longer than 4-hour 0–100% charging) for Gen 5.

 

It is paid subscription. You can get a two-day subscription and download what you want.

As I said, Gen 4 and Gen 5 are practically identical.

 

Do you guys think Ma and Pa Kettle out there will be learning all this about their car battery?
What about a regular Prius in Alaska in the winter, what does it do about the battery?
Even me, who loves his plug in, startsj to think why not a 50 mpg gas car and forget about it after all this detail. I can pay the gas, then it’s over, and the heirs aren’t going to care.

Nothing is wrong, and buying a new one and a used one made weeks apart is pretty good evidence. The used one has lojack which someday I will disconnect. I don’t have the subscription so maybe it’s dead anyway. Maybe it already disconnected. Both cars had/have less miles than yours. Like I said they said more, and more to engineers is .0001%. It may be something then again it may be trivial.
I guess it would be the cp port that is used for the “checking.” It is just so simple to have the values and less writing.

 

Exactly! And the C-rates (charge rates) during regenerative braking or charging by the ICE in a non-plug-in Prius HEV are much, much higher than in a Prius Prime PHEV because of the much smaller battery capacity, making cold or hot temperatures much more perilous!

 

I have the full NCF for Gen 4, which is of course very similar for Gen 5. Unfortunately, I cannot post it because it is copyrighted.

There is a lot in the traction-battery section!

Here is what seems to be going on:

• There is no battery preheating (specifically intended) to protect the battery during cold-weather charging.

• The function of the battery heater that kicks in during charging is to improve cold-weather BEV drivability so that the ICE does not have to kick in—it does not seem to be there to actually help with charging, as there is no mention of that. There is also no mention of charging taking longer or not or the charging current being reduced or not with a cold battery:

(e) Battery Heating Function

(1) As the output of the HV battery assembly drops when the temperature of the HV battery assembly is low,
the engine may start during EV mode even if the state of charge is sufficient. Heating the HV battery
assembly automatically during plug-in charging ensures sufficient output from the HV battery assembly
even in extremely cold environments.​

• However, there is battery precooling for charging—it is to protect the battery during charging:

(c) Pre-charging Battery Cooling Control

(1) Straight after driving, if the HV battery assembly temperature is high when charging begins, the air
conditioning system is operated to efficiently cool the HV battery assembly to prevent high battery
temperatures, especially when the SOC is high, and to minimize deterioration of the HV battery assembly.
(2) The pre-charging battery cooling system can be set to on or off via the multi-information display.
(3) When the battery heating system is operating during charging, the charging time is longer than usual.
(4) When the charging timer is scheduled (departure time) and the ambient temperature becomes higher than
estimated, charging may complete early.
​

(b) Pre-charging Battery Cooling System

(1) When the power switch is turned off and user requested HV battery cooling is enabled, the air conditioning
system operates in cooling mode before charging starts.
(2) Operates when scheduled charging is not set and the temperature of the battery is above the required
temperature. When scheduled charging is set, operates based on the time calculated 30 minutes prior to
the start of charging if the temperature of the battery is above the required temperature.
(3) The pre-charging battery cooling system goes into standby mode 5 minutes prior to operating.
(4) When the pre-charging battery cooling system is enabled and the HV battery assembly SOC is high, to
ensure precise charging, the pre-charging battery cooling system does not operate.​

 

Good Grief...
This is what I was asking about !

Small resistance heater strips under the cells may work fine to keep the pack from getting too cold while plugged in. For 3 days or 31 days, depending.... good, I guess....

But what about a Black Prime parked outside at the Tucson airport in the summer?
While plugged in it will cool the cabin and some of that cool air may get sucked through the battery pack and exit out the back flapper valves.
Is there a time limit on keeping it cooling the pack in this Round-About and wasteful way?

I like 'Sunshade/Vents' on my cars so I can leave the windows cracked open a bit to keep the cabin below ~130°F when parked in the sun.
I guess you couldn't use these on a Prime because you want the A/C cooled air to gently waft through the pack and keep it a bit cooler than ambient.

And what about the Prime not plugged in with either of those situations?
Good Grief...

What is the Degradation amount allowed to invoke a warranty claim on the Prime pack?
In the past, the Leaf had many warranty claims in really hot parts of the country. I wonder how the Prime will do?

For reference:
An unplugged Bolt will cool or heat the pack as required using the pack for power until it gets down to 40% SOC, then it goes 'dumb', like the Prime. It has 'looser' temp ranges when not plugged in.
When plugged in it keeps the pack in a better temp range.

I think a lot of modern BEV's and PHEV's have similar TMS, except for the Prime.

 

​

Refrigerator temperatures are not the ideal range for Li-ion operation. It is better than below freezing, where the battery can safely discharge, but regen braking will be severely limited.

Very low rate charging below freezing is safe, but it is also very slow. The Prime very likely reaches full rate charging before the PiP at the same temps by simply using the heater.

From user reports, it seems this was an afterthought, and is rarely in use. There is no option in settings menus to have it operate by default. To have it operate, temperatures have to be a certain point when the car is parked, and the pop up message asking to use it can't be missed.

The battery fan will run either way, which is a big step up from the fanless Leaf. With the use of a heat tolerant chemistry, it shouldn't be a problem parked in the sun. It just raises the cost.

I believe the gen5 switched to HVAC refrigerant cooling like the Rav4 Prime uses. Can't same what the behavior is when parked, but it is a step up over the gen4.

 

As I said, nothing has changed from Gen 4 to Gen 5 other than the addition of the my-room mode. The relevant sections of the NCF are identical.

As I also mentioned, the C-rate (charge rate) in Gen 5 is twice slower—less than 0.25C (over four-hour charging) as opposed to less than 0.5C (over two-hour charging) in Gen 4—making charging a lot more gentle in Gen 5.

 

But having the battery fan run when the car is in the Tucson sun, but it came from an over-night temp of 90° in the shade,
would not be good.
The Cabin temp can be +130°, maybe. You don't want that circulating thru the pack. I'm sure this TMS has some smarts.

And you're right, chemistry has a lot to do with temperature resistance.

 

A/C precooling before charging turns on the A/C to cool the interior of the car. I am guessing it probably also opens the rear vents to direct the cool air toward the battery.

The traction battery has two blower fans. There is no liquid or refrigerant cooling.

Other than that, the 3.3-kW charger (3.5-kW in Gen 5) under the center rear seat (in Gen 4) has a blower fan to forced-air-cool the aluminum case/heat sink of the charger electronics, which is what you hear during charging.

 

Yesterday I measured my resting battery voltage, 11.7. Charged 12 v couple hours, goes to 12.4. Put my car on120 volt ac to charge the traction battery. The battery voltage goes to 13.1 with everything off. Voltages taken by obd scan tool. Charge traction 1 hour, measure voltage at battery with meter, 12.65. So I don’t know what’s going on. Need to do all readings with meter next time and maybe write it down. I think I did the 13.1 by meter also.

 

sounds like the battery is being drained when off. it could be that the drain is just too much, or the battery health is low