My starter battery died. Confused.

[Tangible]

I had a doctor appointment today, and left my wife in the Clarity in the parking lot, with the heater and other electrical stuff going, for about an hour. The engine was not running. There was plenty of charge left in the traction battery, which was showing 20 miles EV.

When I got back the dashboard was dark, and I couldn’t restart the vehicle. AAA came with a jumper box, and it started right away.

This doesn’t make sense to me, as I didn’t think the starter battery would be draining in that situation. Did I do this wrong?

 

[Boston_Pilot]

I had a doctor appointment today, and left my wife in the Clarity in the parking lot, with the heater and other electrical stuff going, for about an hour. The engine was not running. There was plenty of charge left in the traction battery, which was showing 20 miles EV.

When I got back the dashboard was dark, and I couldn’t restart the vehicle. AAA came with a jumper box, and it started right away.

This doesn’t make sense to me, as I didn’t think the starter battery would be draining in that situation. Did I do this wrong?

Yep, you did. You would have had to leave the car in “drive” to accomplish what you wanted. Only then would it keep the 12v charged from the traction battery. It only charges the 12v while “driving”. This has surprised many people, don’t feel bad.

 

[JFon101231]

Yup, as above.
If it makes you feel better, I once drained the regular 12v battery on my Fit EV because the car continued to try to top off charge during my work day but apparently the plug wasn't fully connected, so it would not charge but the constant "effort" killed the 12v power. I had to explain why I needed to "jump start" my battery car to a colleague...

 

[petteyg359]

Yep, you did. You would have had to leave the car in “drive” to accomplish what you wanted. Only then would it keep the 12v charged from the traction battery. It only charges the 12v while “driving”. This has surprised many people, don’t feel bad.

Anybody have a wiring diagram to fix this (move it from the "drive" button being active to the "power" button) when my warranty expires? Haven't had this problem yet, but it seems like a bad oversight, just like some models failing to limit speed when cruising downhill.

 

[MrFixit]

You would have had to leave the car in “drive” to accomplish what you wanted

Just to be clear.. Your words say "drive", but that can be confused with the "D" Shift Button...
I think you mean that the vehicle needs to be powered ON (as opposed to "accessory" mode), right?
The vehicle should be ON, but in PARK with the parking brake on...

Interestingly, I have found that if you are parked with the vehicle ON in HV mode, the ICE will actually run occasionally in order to maintain the HV battery SOC.

 

[Landshark]

Did the wife survive? What year is your car?

I took a smattering of voltage readings at the 12V battery while the car was parked, unplugged, in Park with the parking brake on and powered up. I then proceeded to turn on the headlights, low and high, seat heaters, rear defroster, cabin heat, A/C, flashers, etc. Voltage ranged from ~14.3-14.8.

From my experience the 12V battery receives a charging voltage under the conditions of my test. Others have parked their car, while in HV mode, and left electric devices on and have reported that the engine will come on to restore lost charge in the HV battery. Similarly, some have connected an inverter to the 12V battery and used it as a back up generator, while the car is parked. One owner reported heating a garage with the car in EV, heater on full and windows down.

Were you possibly in Accessory mode?

 

[Tangible]

Yes, my wife survived. Thanks for asking. She is a mammal, and able to maintain her internal temperature under a variety of circumstances. For this reason, I do not recommend marrying reptiles.

I appreciate the advice, especially the clarification that “Drive” referred to the power button and not the D button. However, I’m pretty sure I DID leave it in that mode, and yet drained the 12V battery anyway.

it’s all very counter-intuitive. Why is the 12V battery even needed to start the car, as there’s nothing to crank? I also don’t understand why I should have needed a jump start from a third party when I already had a massive battery sitting there that (if the engineers had thought about it) would be fully capable of doing the job.

 

[MrFixit]

Everything in this car is controlled by a computer. There really is no "starter".
Even the command to tell the HV battery to charge the 12V battery must be issued by the computer.
The computer operates on the 12V battery, so it is kind of a catch-22.
If the battery dies, then the computer can't tell the HV battery to invoke it's charger.

You might think that while in accessory mode, the computer (while still alive) would recognize that it needs to charge the battery, but Honda chose (probably for safety reasons, maybe regulatory) that 'accessory' was not to be a full-power mode.

Maybe it would have been nice to have some totally manual 'jumper' mode where you could press a special button and jump the vehicle from the HV battery, but again, maybe there are regulatory / safety concerns.

On the bright side, although I don't have one, it should be easy for one of these portable jumper batteries to "start" this car (because there really is no starter). All it has to do is boot the computer. So, that would be a nice (and low cost) accessory to carry...

 

[Tangible]

I think my mistake may have been that I took my key with me, which I presume caused the car to enter a mode in which it was unable to use the ICE to recharge the battery.

So just to recap, the next time I want to turn on my car for use as a warming hut, I press the power button twice with my foot off the brake, and then leave the key in the car.

Right?

 

[Landshark]

I think my mistake may have been that I took my key with me, which I presume caused the car to enter a mode in which it was unable to use the ICE to recharge the battery.

So just to recap, the next time I want to turn on my car for use as a warming hut, I press the power button twice with my foot off the brake, and then leave the key in the car.

Right?

It is my understanding, or misunderstanding, that pressing the ON button twice, without pressing the brake, or pressing it once, while pressing the brake, puts the car in the same mode.

Unless you then press the HV button, the car will be in EV, by default. In EV, the HV battery will charge the 12V battery through a DC/DC converter. It will charge the 12V battery until it is depleted (EV range 0 miles), at which point the car will put itself in HV mode.

In HV, the engine will start to maintain the HV battery SOC set point and the HV battery will continue to charge the 12V battery. The engine never charges the 12V battery directly.

I recommend purchasing at 12V lithium jump pack.

 

[Theoburns]

"ON" mode (two presses of the power switch without pressing the brake pedal) runs everything off of the 12V battery. Neither heat or AC are available in ON mode, you can only run the fan. You can quite easily run down the 12V battery in ON mode. ACC mode (one press of the power switch without pressing the brake pedal) runs only the infotainment system, and it powers off after around 30 minutes. ON mode however has no such timer and will happily let you kill your 12V.

Only while in READY mode is the traction battery supplying power, and the only mode (other than remote climate) that provides heat or AC. The way to check if you have inadvertently put it into ON mode is to look for READY. If it doesn't say READY on the dash, then you are in ON mode. READY mode is really the only mode that should be used while sitting in the car for any length of time. The drain on the traction battery is minimal, although if you are low on EV range and run the heater or AC for an extended period, the SOC will drop below 10%, at around 3% it will start up ICE to charge the traction battery back up around 5%, then shut off again down to 3%, in other words ICE will run for a few minutes every ten minutes or so, depending on the power demand. But as long as you have EV miles that won't happen and ICE will not come on.

 

[MrFixit]

@Theoburns -

Excellent description !!
This should be part of the FAQ, a Sticky post, or similar...

 

[petteyg359]

It is my understanding, or misunderstanding, that pressing the ON button twice, without pressing the brake, or pressing it once, while pressing the brake, puts the car in the same mode.

Unless you then press the HV button, the car will be in EV, by default. In EV, the HV battery will charge the 12V battery through a DC/DC converter. It will charge the 12V battery until it is depleted (EV range 0 miles), at which point the car will put itself in HV mode.

In HV, the engine will start to maintain the HV battery SOC set point and the HV battery will continue to charge the 12V battery. The engine never charges the 12V battery directly.

Also note turning on HV mode and just sitting there will *not* turn on the engine. It is a guaranteed way to get "angry bees" if you want them, though. Go HV, stop and drain a frw estimated miles either by heat or high A/C for 15 minutes, then drive again and listen to it make a manic effort to recover those few miles and get the HV range back to where it was before you stopped. I am curious what the behavior would be if those few miles were all you had left of EV range. Would it kill both the 12v and traction, or would it finally kick on the generator?

 

[Theoburns]

Also note turning on HV mode and just sitting there will *not* turn on the engine. It is a guaranteed way to get "angry bees" if you want them, though. Go HV, stop and drain a frw estimated miles either by heat or high A/C for 15 minutes, then drive again and listen to it make a manic effort to recover those few miles and get the HV range back to where it was before you stopped. I am curious what the behavior would be if those few miles were all you had left of EV range. Would it kill both the 12v and traction, or would it finally kick on the generator?

If ICE is making a manic effort to get back to the previous EV range where it was before you stopped, you can turn off HV then turn it back on again and you will have a new set point. Although this only works if you aren't already down to 0 EV miles.

The system never drains the 12V battery in READY mode, in fact it charges it. There is no scenario that I can think of that would kill or even mildly discharge the 12V battery while you are in READY mode. Accessory and ON modes are the 12V battery killers.

If you only had a few miles of EV range left and you sat parked with heat or AC running, the EV miles will go to 0 (around 10% SOC) and then SOC will continue to decline until around 2-3%, sometimes as low as 1%, before ICE comes on to charge the traction battery. Of course we believe there is a buffer below this so even at 1% SOC you aren't close to actually draining the HV battery. Once ICE starts up at around 2% it only charges the traction battery up to around 4-5% then ICE shuts off again. This cycle will keep repeating as long as you have gas in the tank, thus the traction battery will never "die" in this situation. Worst case scenario is that you run out of gas, if that happens you will be somewhere between 1-5% SOC depending on where you happened to be in the recharge cycle when you ran out of gas. The system will soon shut down at this point to protect the battery, based on a video that I saw where someone ran their EV miles down to 0, then purposely ran out of gas (I mean literally, ICE would no longer run). I think it was a lease car and they didn't care and wanted to experiment. When they ran out of gas they got all kinds of warning messages, but since 0 EV miles is around 10% SOC they still had enough charge to continue driving for several miles. If I remember correctly they started getting warnings that the system will shut down in X minutes, sort of a countdown. But they ended the test by pulling into a gas station so we didn't get to see the system actually shut down.

While all of this is going on, the 12V battery would in no way be affected by these proceedings since you would be in READY mode the whole time all the way up until system shut down. Of course all of this depends on the system performing a timely shutdown prior to total loss of traction battery charge. How much you can depend on it doing its job in that situation I don't know and I don't plan to find out.

 

[petteyg359]

Yes, that is how it behaves *when driving*. Given the guaranteed method for "angry bees", though, the question is if it actually behaves that way when stopped, as OP had.

 

[Theoburns]

Yes, that is how it behaves *when driving*. Given the guaranteed method for "angry bees", though, the question is if it actually behaves that way when stopped, as OP had.

If you only had a few miles of EV range left and you sat parked...

I was talking about stopped. In READY mode though, whereas OP's car most likely was in ON mode without realizing it. Presumably they thought the heater was on based on the fan noise. Then again OP wasn't actually in the car during this time so I suppose those details may not be clear.

The one fact we do know is that the 12V died, as evidenced by the jump start getting things working again (you can't jump start the HV battery). There is no explanation that I know of for how the 12V would drain in READY mode and cause the car to shut off. But the 12V will definitely drain in ON mode, especially with the fan and DRL's running. And maybe the headlights? The DRL's will be on in ON mode unless the parking brake is set prior to turning on the car. Same in READY mode also. Comes in handy if you want to sit parked in READY mode without the DRL's on.

 

[Kerbe]

Why is the 12V battery even needed to start the car, as there’s nothing to crank?

Even Teslas have 12V batteries to power the 12V systems.

When I need to sit with either heat or AC running I put my foot on the brake, power-on the vehicle and leave it in Park - with the parking brake activated. I do this every week when I get my allergy shots - as I am required to stay near the office for 20 minutes following the injections. Today it was cold: I ran the heat and listened to an audio book through the sound system - drained nearly .5 of a mile of range.

 

[JCA]

Yep, you did. You would have had to leave the car in “drive” to accomplish what you wanted. Only then would it keep the 12v charged from the traction battery. It only charges the 12v while “driving”. This has surprised many people, don’t feel bad.

This is definitely not true -- the HV system is charging the 12V battery (via the DC-DC converter) whenever the car shows "Ready" (after pressing the power button with foot on brake). I've verified this a couple times with a voltmeter. It's also charging the 12V battery when the car is plugged in and charging (but not when plugged in and finished or not started charging).

I think my mistake may have been that I took my key with me, which I presume caused the car to enter a mode in which it was unable to use the ICE to recharge the battery.

So just to recap, the next time I want to turn on my car for use as a warming hut, I press the power button twice with my foot off the brake, and then leave the key in the car.

Right?

NO -- that's a recipe for draining the battery; it puts the car in "On" mode without starting the HV system, similar to just turning an ignition key 2 positions (Off->Acc->On) without starting it.

It is my understanding, or misunderstanding, that pressing the ON button twice, without pressing the brake, or pressing it once, while pressing the brake, puts the car in the same mode.

Unless you then press the HV button, the car will be in EV, by default. In EV, the HV battery will charge the 12V battery through a DC/DC converter. It will charge the 12V battery until it is depleted (EV range 0 miles), at which point the car will put itself in HV mode.

In HV, the engine will start to maintain the HV battery SOC set point and the HV battery will continue to charge the 12V battery. The engine never charges the 12V battery directly.

I recommend purchasing at 12V lithium jump pack.

Pressing the power button with foot off brake once goes to Accessory mode -- radio, 12V outlets, and some other things work. Pressing it twice with foot off brake goes to On mode (not to be confused with Ready) -- in addition to those items, the HVAC fan (but not AC or heater itself) works too, meaning it's an even bigger drain on the 12V battery. In both cases the HV system is off and not providing any power via the DC-DC converter.

OP -- are you absolutely sure the car was in "Ready" mode? Leaving with the key should beep warnings but shouldn't stop the car (because, for example, driving away from someone you dropped off who has the key and having the car die in the middle of the road a half block away would be dangerous). What was the temperature outside -- are you sure she was getting actual heat, or just residual ambient air from the fan?

 

[Theoburns]

in addition to those items, the HVAC fan (but not AC or heater itself) works too, meaning it's an even bigger drain on the 12V battery.

And the Clarity's huge DRL's (daytime running lights) will be on also, adding significanty to the drain on the 12V battery while in ON mode. Unless they happened to have set the parking brake prior to turning the car back on, or had Brake Hold active when the car was shut off.

OP -- are you absolutely sure the car was in "Ready" mode?

They most definitely were not in READY mode, as there is no way that the 12V battery will drain and cause the car to shut off while in READY mode, and require a jump start to get the car running again. Think about it, if it could do this while in READY mode then it could happen while driving down the freeway just as easily as it could while parked. But this won't happen in READY mode because the 12V battery is not providing any power in that mode, as you mentioned it's all coming from the DC-DC converter at that time, just as it comes from the alternator in a gas car when it is running.

Another detail that we can fill in that wasn't mentioned is that the car was shut off after pulling into the parking spot, then turned back on (but inadvertently to ON mode) prior to the OP going into the store. If they had parked and not shut off the car and then went into the store it would have remained in READY mode and everything would have been fine.

An easy way this can happen is if someone starts to get out of the car, then decides to turn it back on, and reaches back in and presses the power button, which it will let you do even if you aren't sitting in the car. Although in this case since their foot isn't on the brake the first press will be Accessory Mode. It won't seem to start the car so people will naturally press it again and when they see the dash light up in the familiar looking way they will be satisfied that the car is now running. When in fact it is not running, it is in ON mode, aka "12V Battery Death Mode"

 

[MrFixit]

SOC will continue to decline until around 2-3%, sometimes as low as 1%, before ICE comes on to charge the traction battery

I have experienced the guaranteed Angry Bees (stopped in parking lot for a while, vehicle in "ready" and HV mode, Heater on - causing substantial SOC drop from HV setpoint). When leaving, the bees swarmed (as mentioned, they are easy to terminate by cycling HV off/on if desired)...

However, your description of ICE cycling seems to only apply to the case where the HV battery gets 'dangerously low' (ie:1-3%). I am pretty sure I have also had the ICE cycle with a substantial SOC (if in HV mode) - After all, the 1-3% SOC condition is simply a forced version of HV mode. With a higher SOC, there is a wider window than experienced while driving, but the ICE will come on if there is enough droop. This allows you to conserve charge if desired while waiting in the cold, etc. Can you confirm or deny this case?
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