Dead Battery (for starting the car)

Follow the manual, check that little scope on the battery. What color is it?

 

Doesn't the 12-volt battery run every piece of electronics, all the lighting, and all the accessories except for the heater and A/C (and those fans use 12 volts, too, right?)?

 

The 12v battery is in the system that runs all those things, so technically yes. But, the electricity comes from the dc-dc converter that originates in the hybrid battery and/or the generator. The 12v battery would only last a few minutes if it had to run all the 12v devices without an "external" source of power.

 

This is very interesting and I've always wondered how the 12 v battery gets charged considering there is no alternator nor even any fan belt when I take a look under the hood. So if I'm understanding the discussion, the big battery is charging the 12 v battery via the dc-dc converter so in essence the big battery powers everything 12v in the car via the dc-dc converter and the 12v will always be 100% charged when ignition is turned off? I'm learning something from this forum all the time.

 

As a side note, though we call it a “12V” system and battery, during the few times I actually measured the voltages on circuits when the car was fully on they were about 14.3V.

I think I remember, but can’t completely be sure, that when the car was off (so same circuit was powered by 12V battery) it dropped to 12V.

I assume the dc-dc converter, when on, holds the system at 14.3 V and thereby charges back the “12V” battery in this way. There may be other reasons.

 

Poster @Hi.Ho.Silver used an inverter connected to his Clarity PHEV's 12-volt battery to power parts of his home after Hurricane Michael. @KentuckyKen then asked, "Did you have to turn the car on to have the 17kW hv battery keep the 12v battery full to do this..." and @Hi.Ho.Silver replied, "Yes, the car has to be on in the ready to drive mode to provide power to the 12v battery."

 

@KentuckyKen is your key fob red or is that a silicone cover?

 

ALL automotive and power sport charging systems charge at greater than 12 volts. If you ever check across the battery terminal with a VOM on a running car, you should see 13.5-14.5 volts at idle on a healthy charging system.

Because of the voltage drop in the system, most of the components only “see” or have available to them around 12v depending on the vehicle.

-Skip


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It’s actually a purple silicone cover. It was a freebie from my dealer. I think the brand is The Jacket. Fits perfectly but doesn’t cover the chrome at top where the key ring is. I have it in my spare fob and use a Lexus leather cover on the fob I pocket (another freebie, boy am I cheap!) that keeps the chrome top from being scratched.

 

I accidentally left my lights on and drained the 12v battery overnight. When I went to my car in the morning the dome lights wouldn’t go on and the car wouldn’t start. I connected a jumper cable to the car just like I would do for any other car and was able to start the car and charge up the 12v. Does anyone know a way to “jump” the car from the 17kw battery? That one still had a full charge but a couldn’t use it to get the car started. I guess it’s good that it was protected from my stupidity that caused the 12v to drain.

 

So apparently it means that the 17kw battery does not keep the 12v battery charged up when the car isn't on? Reason I ask: when leaving the car for a few weeks in the garage should I have my battery tender on the 12v battery?

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@Hi.Ho.Silver reported that when he used his 12-volt battery as a home power source during Hurricane Michael, he had to leave his Clarity ON to get the big battery to keep the small one charged. Some posters have speculated that it's possible the Clarity can send a small charge to the 12-volt battery without the car being ON, but probably not enough current to offset the drain from the LED headlights (didn't you get an audible warning?). The car's substantial 12-volt battery should easily retain its charge a couple of weeks without a trickle charger.

 

Do you see any downside with having the 12v trickle charged (because of the PHEV system)? I'm going to be down south during the depths of (zero degree F temps) winter. Can't find any info if the fact the car is a PHEV if would change charging like an ICE car.

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Other than a lightning strike, I don't believe there would be any problems associated with using a trickle charger, but smarter members of this forum may believe otherwise.

 

Based on posts and my checking the battery, I think the verdict is still out as to exactly what happens to the 12v battery when the car is off.
Immediately after driving, I measure the voltage around 13 v, and 12 hours after charging (not turned on) around 12.5v. I left the car garaged for 11 days turned off and it measures 12.1v.
We need more observations on this to figure it out. If the Clarity treats the 12v battery like a regular gasmobile does and just lets it sit there, then it’s going to eventually run down since most all modern cars have a parasitic drain when off. The question is, if that’s the case (and that’s a big if) will it sense the low voltage and at some point charge it if the HV battery is not below some threshold?? Does having it plugged to an EVSE make any difference in this behavior?? I don’t think we know for sure yet. I await the more expert among us for enlightenment.

At my present level of understanding, I would use a trickle charger or battery minder if I was going to let the car sit for more than 2 weeks (maybe less if very cold?).

 

I can tell you that leaving the lights on all night resulted in a dead battery that had to be jump started. .

 

I'm assuming that the car was not plugged in?

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No. It wasn’t plugged in. Not sure I want to test this again with the plug in - but I’ll think about it!

 

I hear you! I’ve already tested the HGDA (Honda garage door avoidance system) and it didn’t work. Don’t want to test it again. I did accidentally test the water tightness of the key fob and it made it through a wash and extra rinse cycle, but I’m not testing that again either. LOL at myself.

 

Got it. Please don't (test it again by leaving the lights on) do it on my account.

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