12 volt battery on 2018 clarity plug in

Quite likely your 12V battery has failed. If you are still under warranty (3Y / 36K), get to the dealer for a free replacement.

 

Sounds like you need a new battery.

 

I have pretty much the same situation - my 12v battery was dead this morning after the car being charged overnight from level II 240v charger.
The exact same event happened 3 weeks ago, I took my car to the dealership who said no problem found, the 12v battery in great shape.
At this time I am going to bring it back to the same "stealership" and insist to check the DC-DC converter which is responsible for charging a 12v battery from the main, high voltage battery.
I would guess you may have the same situation with your car.

 

If you have a digital voltage meter you can check the voltage at the battery when the car is ON/READY. It should read 14.x. That would indicate that the DC/DC converter is functioning properly.

Measure the voltage before turning on the car, ideally after the car has sat for a few hours without being charged. Resting voltage should be ~12.7.

 

And because the 12v is under the hood, leaving it up/open will not activate any systems when one comes back to check the voltage reading. TIP: don’t have a FOB nearby either.

 

The car was inoperable due to 12v depleted two times last week. Both times it left overnight being charged and plugged in, and both times the 12v battery showed ~7v when I measured it after not being able to start the car.
The DC-DC converter is doing its work - while the car runs on HV mode it shows 14.55V on the 12v battery, 13.5v while it actively charges the main HV battery.
A voltmeter logger showed the voltage drops by 0.2V or so every hour, and this process started 3-4 hours later after the HV battery was fully charged, and the car was still plugged in.
I took the car this morning to my dealership service, but I am very doubtful about their ability to find the culprit.
Anyone else experienced the same?

 

You should take a picture of the voltmeter showing 7 v. Maybe the battery capacity is fine but you might have something draining the battery.

 

Based on the evidence you presented, and in spite of the dealer claiming that your battery is "in great shape", I don't beleive it.
I think your battery has died. My thought would be to take it to your local auto parts shop. They will happily do a load test on the battery and prove / disprove whether the dealer's claim that it is "in great shape" is true.

If your battery really is "in great shape" then there is something much more serious going on, and Honda will wind up sinking much more money into your car (hopefully you are still under warranty). If their diagnosis is questionable, then it may still be in their best interest to 'try' replacing the battery before they launch into a more difficult diagnostic procedure.

You dont have any aftermarket devices installed that could be draining the battery excessively (like a dashcam, or other) do you?
How old is your car? Are you still under warranty?

 

I sure did provide that picture to my service advisor, they tested the battery and said it is in great shape. I also got the battery tested by Autoze yesterday with the same result. Obviously, there is something draining the battery. As a wild guess, I will contact the charger manufacturer and see what they say.

 

What do you mean by this? The "Charger" is Honda...
It is the vehicle itself that charges the battery (not the EVSE that connects you to the wall).
If it is not charging correctly, then the problem is entirely within the Clarity.

 

I have JuiceBox 40 Pro, just spoke with them here is what they say - since I have two chargers (need to charge the Clarity and Tesla simultaneously), I have set up so-called load balancing (both chargers would operate from the same, shared outlet and would not exceed a maximum rated amperage -50A )
According to them, the car is sensing/testing the state of plugged voltage supply and using a 12v battery to do so, therefore MIGHT deplete the 12v battery within some period of time. Another user reported the same problem a week ago. They updated the load balancing algorithm 3 weeks ago and it is the exact same time when my problems started! So, now they are working to rectify the issue. Looks like a poor design decision.
Hopefully, it will be fixed soon, but for now, I have to unplug the charger as soon as it is finished charging the Clarity.
Just wanted to share this, so another person won't waste time and spin the wheels.

 

That’s an interesting set up you have. Another possible work around would be to revert to L1 charging the Clarity on a separate outlet. If you have the time, overnight, that might be a less inconvenient option than physically unplugging the cable at the end of each charge cycle.

I can’t say for sure, but it seems that the “sensing” would stop operating when the 12V battery reached a certain voltage, say 10.5V. If so, then the Juice Box theory may not full explain the battery voltage dropping to 7V. I would also add that a 12V battery that has hit 7V on several occasions might be a battery that is in questionable condition.

 

Thanks for the idea!
I would rather have an inconvenience dealing with unplugging a charger than switching to the L1 charger. This car is used by my wife and she does not always remember to plug it in (yes, a push notification about her car not being charged after a certain time is ignored, so I had set it up on my phone) and L2 gives us the ability to charge quickly if it was missed.
Another suggestion from JuiceBox support was to remove a load balance group and set a fixed current limit for each box. This is what I would try and see if it works.

 

It seems surprising that they are telling you that the Clarity 12V system is constantly testing the voltage supply of a connected EVSE in this situation, even when you are not charging. We know that the 12V system is needed for charging, from the experience of people with a weak or dead 12V battery who cannot start charging. But I would think that the 12V system only starts sensing/testing the voltage supply when a charge session is about to commence, like when a scheduled charge session begins, or the fob is pressed, or for most people when they plug the car in. If it was sensing/testing the supplied voltage the entire time the car is plugged in even when not charging, then yes you would expect the 12V to eventually run down as during that time it is not receiving power from the DC-DC converter.

So clearly it does not normally do this, and they seem to say the same thing by suggesting to try fixed instead of balanced. But how does the fact that the Juicebox is setup for balanced cause the Clarity 12V system to constantly check the power coming from the EVSE while plugged in? My understanding of what the Juicebox does is if one car starts charging using one of the Juicebox EVSE's, it lets that car have the full current. But if a second car starts charging with the other Juicebox EVSE, then it reduces the current going to each car. But that all happens only when charging, or starting to charge. But just having the EVSE charge cable plugged into the Clarity but not charging, why would the Clarity start constantly sensing/testing? Unless as you theorize that it is a glitch in the Juicebox balancing software, maybe the Juicebox keeps constantly "pinging" the Clarity that it is about to start charging even when it isn't and that is keeping the 12V system active?

 

I tend to agree with this. On a few occasions I have plugged the cable into the port when I knew the battery was fully charged. The light blinks a few times and goes off. This would suggest that nothing is happening.

 

I started experiencing 12v battery issues ~33 months into ownership. The same symptoms OP described. Had the battery tested at the dealership and replaced under warranty with a much better honda OEM 100 month battery.

Before I went to the dealership, I got it tested in 5 minutes at my local autozone for free who verified my battery needed replacement. You can do that to get a 2nd opinion if you don't agree with your dealer although they don't replace it under warranty unless their test shows its bad.

 

JuiceBox support said that seems to be a poor vehicle design, they are working on a workaround and will push a firmware update to address this issue.
At this moment, the Juicebox keeps constantly "pinging" the Clarity that it is about to start charging even when it isn't and that is keeping the 12V system active till the 12v dies.

 

I am still not following their logic. They admit that the Juicebox keeps constantly pinging the Clarity that it is about to start charging even when it isn't, but that it's the Clarities "poor vehicle design" for believing the Juicebox each time it gets this message? Is the Clarity supposed to figure out after the tenth false alarm that the Juicebox is lying and then go back to sleep? Maybe that is what other cars do as a workaround for poorly designed EVSE software. Or else maybe they are saying that other cars use less 12V power to monitor the voltage while not charging?

Then again this is their theory for how their system could possibly cause your 12V battery to die, since you asked them about it, although I don't think it has been proven yet that the Juicebox is the actual cause for your 12V problem?