12v auxiliary battery charging

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FMIB
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Post by FMIB » Sun Sep 19, 2021 4:28 pm

Not sure this has been answered previously and before we hit winter when the car might remain on the drive for several weeks at a time, how is the 12V auxiliary battery charged to stop it going flat?
If I plug into a charger, with the car switched off and locked, does charging the main battery also charge the auxiliary battery or does the car need to be switched on and in motion before the main battery charges the auxiliary?

On my previous cars, I use a CTEK battery charger in the winter to top up the battery when the car is not used, always leaving the battery connected in the car. Can the same procedure be used on the Honda or is it absolutely necessary to disconnect the battery leads before charging?
I read that the battery must be fully disconnected when charging, which would be rather inconvenient on a modern car.

Fakeplasticman
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Post by Fakeplasticman » Tue Sep 21, 2021 2:01 pm

some good info on it here from what I recall

viewtopic.php?f=11&t=616

FMIB
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Post by FMIB » Tue Sep 21, 2021 4:46 pm

Thank you, that’s helpful, even if I need to read the detail several times and try to understand when and how to keep the 12v battery charged, avoiding the “it won’t start” over periods of non use

5thcivic
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Post by 5thcivic » Tue Sep 21, 2021 7:38 pm

After reading the posts here I charged my battery with an intelligent charger with no problems. The battery is 45Ah and I just connected the charger in situ even though the manual says to disconnect the battery, obviously with the e off. The charger is only 4 amp and have used it on various Civics without disconnecting for years without a problem (Civic manual also says disconnect). In fact I've used spade terminals to permanently connect the special socket for the battery charger I have on the Civic for long term trickle charging. This has one advantage of never seeing any small sparks when messing with big crocodile clips. Both cars do low mileage so a trickle ever now and then won't harm.

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ChesterUK
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Post by ChesterUK » Sun Dec 05, 2021 10:07 am

My wife attempted to access her car on Tuesday last week. It was totally dead and unresponsive, the one day that I was away from home that week! As soon as I got home on Wednesday, I gained access to the car via the key, got under the bonnet and disconnected the car from the negative battery terminal. Upon connecting a smart charger, it started charging at <0.2A and steadily started increasing to about 2.5A over a 20 minute period. It was clearly in a deep state of discharge. After 30 minutes I swapped to fast charging which is just under 6A. A total of 3 hours later the charging rate had dropped below 5A and it started to rain. Not wanting to leave the extension lead outside (although I could have simply 'bagged' it) I stopped charging and connected the negative side. The indicators started to rapid flash and wouldn't stop until I used the fob to unlock the car. The systems needed time to initialise (a few minutes) to get time, GPS, etc, but the car has been fine since.

The reason all this happened is we had some time off and the car was not used for 7-8 days. I know the MX-5 ND can have similar issues, so this is nothing unique to BEVs! I'm very tempted to fit a CTEK monitor/trickle charger, but I just find the situation totally nuts when there's a 7kW charger just for this car costing 900 quid! My wife has not as yet contacted the dealer to complain (sending an email today).

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EEEE
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Post by EEEE » Sun Dec 05, 2021 11:24 am

It does seem slightly bonkers that the 12v system isn't charged when mains is available. Why it only chooses to do so when the car is 'on' is beyond me...
'21 e Advance - Charge Yellow - E1702RR alloys
'17 Civic Sport CVT
'00 Prelude 2.2VTi

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londiniumperson
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Post by londiniumperson » Sun Dec 05, 2021 4:54 pm

ChesterUK wrote:
Sun Dec 05, 2021 10:07 am
My wife attempted to access her car on Tuesday last week. It was totally dead and unresponsive, the one day that I was away from home that week! As soon as I got home on Wednesday, I gained access to the car via the key, got under the bonnet and disconnected the car from the negative battery terminal. Upon connecting a smart charger, it started charging at <0.2A and steadily started increasing to about 2.5A over a 20 minute period. It was clearly in a deep state of discharge. After 30 minutes I swapped to fast charging which is just under 6A. A total of 3 hours later the charging rate had dropped below 5A and it started to rain. Not wanting to leave the extension lead outside (although I could have simply 'bagged' it) I stopped charging and connected the negative side. The indicators started to rapid flash and wouldn't stop until I used the fob to unlock the car. The systems needed time to initialise (a few minutes) to get time, GPS, etc, but the car has been fine since.

The reason all this happened is we had some time off and the car was not used for 7-8 days. I know the MX-5 ND can have similar issues, so this is nothing unique to BEVs! I'm very tempted to fit a CTEK monitor/trickle charger, but I just find the situation totally nuts when there's a 7kW charger just for this car costing 900 quid! My wife has not as yet contacted the dealer to complain (sending an email today).
This has happened to me once in a similar situation where I hadn't used the car for about a week.
It also happened last weekend (though this time self inflicted) when I was cleaning the interior and must have left it accessory mode & not fully ON or fully OFF. The solution was to use a 12v battery charger & after about an hour I was able to power on the car and went for a 10 minute drive before plugging the main traction battery in an attempt to top up both the this and the 12v battery.
Mine also was having a hissy fit for a while with the rear lights flickering for a while when the 12v battery was charging.
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FMIB
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Post by FMIB » Sun Dec 05, 2021 5:12 pm

I think its even more bonkers that these EV cars are draining a 45Ah battery in 7 or 8 days. Whilst I know there are lots of things in a car that are active when switched off, slowly draining a battery, but +/- a week is madness.
So you go on holiday, leave the car parked at the airport for a week and risk being unable to drive home, wonderful.
I often leave mine for a week or more between use, touch wood, no issues so far

5thcivic
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Post by 5thcivic » Mon Dec 06, 2021 3:47 pm

I've not the one week problem above but do not use either the Civic or the E much during winter. I can report that in addition to my other smart 12V charger I bought the Lidl one at £15 just for the E (micro control, over voltage/current/temperature protected etc) with some SAE connectors from Amazon. Connected a permanent wire on the E, and replaced the croc clips on the charger. No problems trickle charging with battery still connected to E with the E off and locked and the main EV charger not used (I would NOT try connecting both at the same time).
I too find it strange the main charger does not trickle the lead battery, there must be some valid engineering reason not to do so, otherwise it just seems idiotic.

Jan44
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Post by Jan44 » Mon Dec 06, 2021 4:37 pm

I haven't had that problem, but I bought a neat little Lidl charger. My question is: Is ity essential/desirable to disconnect the battery from car before attaching charger?

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