Flat battery on a new car with Yuasa battery

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Post by green1 »

You mean you fastened the seatbelt before you left the car / offed it?

I doubt that has an impact when the car is off, although it should do when the car is on. If cleaning with the car on, I do keep the seatbelt fastened so the car is in ready.

Could be worth doing a few times to see if there’s any repeatable pattern there.

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Post by MrM83 »

green1 wrote: Fri Jun 07, 2024 7:49 pm You mean you fastened the seatbelt before you left the car / offed it?
Correct. I was surprised to see the 12v battery charging when the car is locked and “dormant”.
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Post by EEEE »

I have seen the car charge the 12v if it is flat and you unlock/lock it. This happened after a recent 2 week holiday when I was expecting the car to be flat. I unlocked and locked the car without getting in, then noticed via the bm2 it was charging. The car was left at home (far to useless to get to the airport or take the luggage required lol).

My linked post is the only occurrence 12v charging that we know about as a result of no external stimulus.
'21 e Advance - Charge Yellow - E1702RR alloys
'17 Civic Sport CVT
'00 Prelude 2.2VTi
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Post by MaXPainT »

Sounds like something in the car needs to wake up for the car to check the 12v battery and start charging. Locking/unlocking, probably, triggers this wakeup. I wonder if it can be triggered automatically with a preconditioning or something. I assume you can unlock/lock the car via the app, but many of us don't have the luxury.
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Post by 5thcivic »

Posted this a couple of years ago:
"I usually trickle the 12V battery once a week or fortnight since do not do many that trips for the main battery to recharge it. I usually use one of those simple led indicators to see what state it is in and it never is full but always shows middle led as "needs charging" but never the low led.
I had not used the car for nearly three weeks since in the process of selling my other one so thought I'd better charge the battery.
Coming to the car the door handles did not pop out, so I had to unlock via the key and not sure but I don't think all the dash came up straight away.
Then it did and showed 76% on the main battery.

Opened the bonnet and checked the 12V and the top led of "fully charged" lit. I had never seen this before from cold, only immediately after charging or a longer trip.
I checked with a multimeter and the battery was 14.2V accompanied by a humming from the system."

So it looks like the HV can top up the 12V in certain circumstances.
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Post by s2ke »

Yes. It doesn't charge on an alternator so closing your seatbelt will see 14.5v on the 12v (charging)
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