12V battery issues

[Rew1mac]

The problems with Honda e 12v battery show fundamental errors in design strategy.
Contrast previous cars that I have owned. The best were Scandinavian. When the engine was stopped and key removed, all ancillary devices stopped except alarm. This ensured battery protected, ready for re-start.
Regulatory authorities should mandate good design of electrical systems, so that motorists are not stranded in difficult situations.

[EEEE]

The problem with that idea is that the complexity of such cars warrants circuits to always be live.

Otherwise, we would just have the cars of yesteryear (Feature wise). No bad thing if you ask me as far as hondas are concerned!

The problem with the E is that the infotainment is part of the always on system. The entire operating system stack is just too complex to guarantee it will always work as expected. Honda don't design or build it. Whilst they should test it, any software developer will tell you its an iterative process, a never ending long tail of cost vs reward that only diminishes. This never happens if its 2 different companies as the system is delivered as a contract/set price with very little ongoing support (as is evident from the scant updates we have seen).

The 12v battery is just too damn small as well. The owners manual lists the 45ah battery as a 34ah rating at 5hour discharge. Given that it can go flat in well under an hour, the current draw must be excessive for what a small starter battery is designed to give out. This is why Tesla will always win out in any EV design - they own the whole stack completely of hardware and software, and the cars will always be lightyears ahead of anything else (technology wise).

[Rew1mac]

Honda-e, late 2020.
Car failed to respond to power on button after 3 days parked outside home.
When last used, main traction battery was 74%.
Checked ancillary battery, only 2.4 volts.
Disconnected and charged battery for 5 hours, until 12.9 volts.
Reconnected 12v battery.
Moved car under cover and connected ac charging cable.
Confirmed all accessories off.
After 24hr, disconnected charging cable.
Checked ancillary battery again. Surprised to find reading had fallen to 12.4 volts.
Why?

[FDAD]

Honda-e, late 2020.
Car failed to respond to power on button after 3 days parked outside home.
When last used, main traction battery was 74%.
Checked ancillary battery, only 2.4 volts.
Disconnected and charged battery for 5 hours, until 12.9 volts.
Reconnected 12v battery.
Moved car under cover and connected ac charging cable.
Confirmed all accessories off.
After 24hr, disconnected charging cable.
Checked ancillary battery again. Surprised to find reading had fallen to 12.4 volts.
Why?

If the battery dropped to 2,9v it's dead for good, even if you can get it to «working» condition it will never sustain a good amount of charge for very long.
My advice, new one.

[EEEE]

Honda-e, late 2020.
Car failed to respond to power on button after 3 days parked outside home.
When last used, main traction battery was 74%.
Checked ancillary battery, only 2.4 volts.
Disconnected and charged battery for 5 hours, until 12.9 volts.
Reconnected 12v battery.
Moved car under cover and connected ac charging cable.
Confirmed all accessories off.
After 24hr, disconnected charging cable.
Checked ancillary battery again. Surprised to find reading had fallen to 12.4 volts.
Why?

Main traction battery is not relevant to 12v battery at all. Ultimately it is the source of the 12v charging, but unless your traction battery goes flat, it is of no concern.

2.4v is flatter than a pancake, and most likely its damaged/will never be as good again (in terms of stored capacity, resting voltage etc).

5 hours charging isn't long enough if the battery was in decent condition. Charger may say its done but it doesn't really know. That's the first clue the battery is now knackered.

Lead Acid batteries have a slow reaction time. The voltage will drop after charging considerably. The resting voltage of a decent fully charged battery is around 12.8v depending on temperature and construction. The OEM battery once its gone flat a time or two, seems to rest at 12.5 or less which is poor.

The OEM battery, even when finished charging at 14+v , it will slowly drop over a period of 8 to 12hours to its natural resting voltage. My 12v was also discharged on more than 1 occasions, its resting voltage was also a little on the low side compared to a new Yuasa battery. Further tests on the Honda OEM Panasonic battery revealed it doesn't even hold half of its rated capacity anymore. Once flattened, its more likely to give you problems again.

Likewise, when the 12v is discharged by some load, even for a minute only, it will take up to 30minutes to recover back to its natural resting voltage. This is clear to see if you use a battery voltage monitor/logger on the e. The car wakes up, the voltage drops .1 or .2v for a minute or two (indicating some load), and then a half hour recovery back to where it was resting previously.

Giving the complexity and poor integration of the various modules, it will take us all some time to track down the exact cause(s) of what drains the battery.

Guesses so far are:

Infotainment not going to sleep.
Infotainment waking up (in response to the notification for software update or some other TCU message).
Door handle microswitch issues.
as of yet undiscovered issues...

It is annoying for sure...

[Rew1mac]

EEEE, you are correct. In the days following, ancillary battery voltage continued to drop and needed repeat charging.
The car needs to go to local Honda dealer for diagnostic check before spending money on a new 12v battery.

[EEEE]

I suspect like most you will have an issue with one of the door handles, which contain a couple of microswitches. These appear not to be the most waterproof of items, leading to shenanigans with the windows or handles. Not conclusively proven yet.

Out of interest, do you have an orange circle with a 1 in it showing on the top right of the infotainment screen? If so you have a pending software update, and you will need to link the car to wifi to download it. There is some evidence that the pending update prevents the infotainment from going to sleep.

[hurricaneh5]

Morning everyone,

First issues with 12v Battery after 2 years ownership. Been on the forum a few times but thought I would share and join today.

Short story is sorted just be careful as RAC blew the 175a fuse.

Long Story:

I use the e regularly and probably have highest mileage on here 55k nearly… had no issues until left the car for a week and came back to it. Surprisingly it worked but got home plugged in for octopus charge and it didn’t and was dead am the next day.

Rang RAC initially as it’s with the bank and our lass was out in the other car and I needed the e, took hours, eventually they came and were very poor and in rush. Diagnosed what I knew a knackered battery and said get a new one

So thought I will trickle over night and remembered I have hondacare so AA turned up this am and deduced rac had blew up the fuse and they rectified it until I get Honda part.

So now I’m after a new battery anybody recommend anyone specific? was looking at Bosch s4 021 45ah about £60.

Thanks in advance Nick

[londiniumperson]

So now I’m after a new battery anybody recommend anyone specific? was looking at Bosch s4 021 45ah about £60.

As you have found out, this is the result of connecting a jump pack the wrong polarity.
Have a read of this thread, it shows a couple of 12v battery replacement options:
Panasonic 12v OE battery testing

[hurricaneh5]

Thanks for the link…. Pulled the trigger on the Bosch, now got the black screen of doom and no audio .

Anyway read that it’s probably the anti theft according to manual but will run to work and see how it goes….

Tried the audio fuse 19 trick no joy so hoping for more insight…