12V battery failure

[Joolsdc]

Used my 12V electric pump to inflate the four tyres by 0.2 bar each. When finished I realised the whole car was dead.
I knew the traction battery was charged to about 80%
So the 12V battery must have been drained.
Luckily I have an old battery charger that was pushed into service
Left for a couple of hours, this was able to charge the 12V and I was able to start the car.
In the meanwhile I’d called my dealer who suggested bringing the car in to have the battery checked. Or I could call Honda Assistance.
I took the car in. Battery checked. No problems
Their e engineer suggested the issue was that I had not “turned the car on”, so was just pumping up the tyres via the 12V battery. If I’d turned the car on, then charge from the traction battery would have recharged the 12V battery. Hmmm
Thoughts? On the one hand it makes sense - a bit like running an ICE to run the alternator to charge the 12V. But on the other hand, why doesn’t the traction battery just trickle charge the 12V anyway?
I will keep you posted and appreciate any views
Happy New Year

[londiniumperson]

Used my 12V electric pump to inflate the four tyres by 0.2 bar each. When finished I realised the whole car was dead.
I knew the traction battery was charged to about 80%
So the 12V battery must have been drained.
Luckily I have an old battery charger that was pushed into service
Left for a couple of hours, this was able to charge the 12V and I was able to start the car.
In the meanwhile I’d called my dealer who suggested bringing the car in to have the battery checked. Or I could call Honda Assistance.
I took the car in. Battery checked. No problems
Their e engineer suggested the issue was that I had not “turned the car on”, so was just pumping up the tyres via the 12V battery. If I’d turned the car on, then charge from the traction battery would have recharged the 12V battery. Hmmm
Thoughts? On the one hand it makes sense - a bit like running an ICE to run the alternator to charge the 12V. But on the other hand, why doesn’t the traction battery just trickle charge the 12V anyway?
I will keep you posted and appreciate any views
Happy New Year

This is a common issue on BEVs, it happened on mine on the day of collection before I had even driven it whilst the dealership failed to get the TCU setup for the app
If you are feeling generous then it could be for safety issues, more likely that it was two discreet teams that each worked on the HV & 12v systems & they didn't consider the whole car in it's entirety.
I have set mine to auto power on when I open the car so this doesn't happen to me.

[Isow]

Your battery hasn’t failed, it’s just discharged .

[555djx]

I have set mine to auto power on when I open the car so this doesn't happen to me.

I have mine set to the same but I read somewhere in the manual that, even though the car is turned on automatically on entry, the car isn’t in ‘ready’ mode until you press the brake pedal, nothing else just the brake pedal, at which time a car symbol with a left/right arrow underneath appears on the dash screen. I’m therefore assuming that the traction battery isn’t engaged until that symbol appears, and that until that time it’s in ‘accessory’ mode and running off the 12 volt battery only.

I’m certainly interested in the opinion of others about this.

[omara500]

My 2017 Leaf tops up the 12v battery when the car detects a dip in voltage. It’ll charge it up even when left parked in my driveway. Makes sense given the common 12v battery dying scenario is when a car is left unused for a while in the winter...

[iHansz]

I have mine set to the same but I read somewhere in the manual that, even though the car is turned on automatically on entry, the car isn’t in ‘ready’ mode until you press the brake pedal, nothing else just the brake pedal, at which time a car symbol with a left/right arrow underneath appears on the dash screen. I’m therefore assuming that the traction battery isn’t engaged until that symbol appears, and that until that time it’s in ‘accessory’ mode and running off the 12 volt battery only.

I’m certainly interested in the opinion of others about this.

Always find it very difficult to see if the car is "on" (I know, the left/right arrow). At some point you get the message that he wants to switch off to save the battery? But which battery? That big one has power enough... Very confusing. Always afraid to drain the 12v battery.

[HausO]

I have a similar problem (see viewtopic.php?f=11&t=616).The charging logic of the 12V is not documented in the manual. Honda Germany and my local dealer are not able to answer my questions.

My knowledge base on observation and measurements is the following:

12V battery is never charged when "ignition" is off. Two days ago I killed the 12V battery within 10 hours because parking lights were on. SoC of HV battery was about 60%. The onboard charger for the 12V system was not activated.

The 12V battery is not charged every time while driving like in a old car with a normal generator. If I charge my car to 90% and more SoC, the 12V battery will not be charged. If the SoC is lower than about 90% when I start the car the 12 battery will be charged.

The Honda e seems to have a BMS for the 12V system (small sensor at one battery connector with additional cables) but the information is not provided to the driver and the logic for charging is not constructive. (12 x 35Ah = 0,42kWh for 10 hours with parking lights on. => about 1,2% SoC of HV battery => enough energy for 500 hours > 20 days).

[Prasher]

I have a similar 12v battery drain issue but Honda UK has not been helpful in explaining why this is as no lights are left on. I have had to call roadside assistance 3 times to jump start the car.

[advance2020]

I have a similar 12v battery drain issue but Honda UK has not been helpful in explaining why this is as no lights are left on. I have had to call roadside assistance 3 times to jump start the car.

Prasher: thanks for posting here.
This is our twitter exchange in full for others.

I personally have never had any problems, but clearly this is a “worrying issue” if it is a general fault/weakness of systems. I don't fully understand when and how 12V is charged, but I will check condition of my battery. I note Owners Manual states that Both Battery terminals should be disconnected before charging battery (using a battery charger).

I often leave my car (garaged) unused for several days. Never see drop in main battery %. As yet, have had no problems with 12V that I’m aware.

[advance2020]

I have set mine to auto power on when I open the car so this doesn't happen to me.

I have mine set to the same but I read somewhere in the manual that, even though the car is turned on automatically on entry, the car isn’t in ‘ready’ mode until you press the brake pedal, nothing else just the brake pedal, at which time a car symbol with a left/right arrow underneath appears on the dash screen. I’m therefore assuming that the traction battery isn’t engaged until that symbol appears, and that until that time it’s in ‘accessory’ mode and running off the 12 volt battery only.

I’m certainly interested in the opinion of others about this.

Hi 555djx
I am hoping by now you are more familiar with your “e” as you should be able to jump in and go. When you enter your car, carrying your smart key, it will wake up, and when you close the drivers door, it will fully power up. Press brake pedal and release electronic brake, press D drive and away you go. I also select One Pedal Mode and Select Safety Config to disable RDM Road Departure Mitigation.

I highly recommend driving in One Pedal Mode, as it enables the Auto Brake function. This makes stopping at junctions, traffic lights etc a doddle. No need to do anything. All controlled by your right foot.