12v Battery Maintenance

[JoDa]

Hi All. After a 6 week holiday we came home to a completely flat 12v battery. The AA got it going after a jump start and we took the car to our local dealer who checked it over, charged it up and found no faults. They just put it down to lack of use which is fair enough but we do these 6 weeks twice a year and don't want a repeat. I've looked at battery maintainers but the Honda manual states you should disconnect the battery first before charging. I'm reluctant to do this for security reasons as the car is left on the drive.
Has anyone out there used a maintainer or charger succesfully without having to disconnect the battery first?.. 2022 Ex Style.. TIA

[coldstart]

I wouldn't worry too much about not disconnecting the battery. I've seen cars in the Honda dealer's showroom branched to a charger and the battery was connected. Just make sure, you use a high quality charger which never exceeds 15V output!

btw: Did you lock the car during your absence? - Modern cars can drain the battery within a weeks time if left unlocked because the electronics never shut down.

[Kremmen]

Agree on both points

I've never disconnected my battery and used a CTEK on it every few weeks if I don't use the car, never had any issues

I was told by a Honda employee that you should always double lock the car as that shuts down all the unrequired circuits

Fortunately mine is in a powered garage so I'd be setting up a Kasa/Tapo smartplug on the connected CTEK and time it for a 5 hour charge every 2 weeks which is how long mine takes to fully charge if left for 2 weeks

[5thcivic]

Ditto on the double lock.

I've charged the Jazz, the E (the 12V battery) and 5 Civics all with the battery connected many hundreds of times over the years with no problems, just use a good micropocessor controlled protected charger.

[HertsHonda]

I frequently think back to last winter when a combo of cold weather, investigating a headlight problem (turned out to be a fuse!) a bad cough and Covid, Caused my Mk3 Jazz to be idle for several weeks!!
When it didn't start, disconnected battery and charged. Suspect that messed the Auto Idle Stop/Start -'cos it's still U/S!! :-{(    Think I should have put just enough charge in via charger to start, then let the alternator top it up.
Maybe then the (too) clever battery status system would recognise the discharge had been made good. 

[Jocko]

I have a SMART charger connected to my Fabia constantly. I only unplug it to go somewhere. I did the same with the Jazz from moving in here on Aug 21 until parting with it on Jan 23.

[Jazzik]

Ditto on the double lock.

The same here. Always (and I mean ALWAYS) on the double lock plus switch off the key fob.

[ColinB]

Bit puzzled by all this (from an academic  viewpoint 'cos I don't own a Mk4). Elsewhere in the forum, I think someone has pointed out that the handbook says you should drive the car for at least 30 minutes every 3 months in order to keep the HV battery happy. By implication, the 12v battery ought to be OK with that, otherwise surely Honda would specify something different? So if it drains quicker than that, isn't there a fault? And if you have to keep the car trickle-charging when not in use, are you not simply disguising that fault?
I've never trickle-charged my Mk3, and once left it for nearly 7 weeks; it started first time.

[coldstart]

@ColinB: I think, you are misrepresenting the manual. The relevant section you mentioned is about the high voltage battery, not the 12V battery:

High Voltage Battery

The High Voltage battery gradually discharges even if the vehicle is not in use. As a result, if your vehicle is parked for an extended period of time, the battery charge level will become low. Extended periods of time at a low state of charge will shorten battery life. To maintain the battery state of charge, drive your vehicle for more than 30 minutes at least once every three months. Extreme high temperatures can affect the battery life. You can minimise the effects by parking the vehicle in the shade during the summer.

The 12V battery is recharged by the high voltage battery but only if the car is used!

Addendum: Quote is from p400 of the online MY24 manual

[ColinB]

@ColinB: I think, you are misrepresenting the manual. The relevant section you mentioned is about the high voltage battery, not the 12V battery:

High Voltage Battery

The High Voltage battery gradually discharges even if the vehicle is not in use. As a result, if your vehicle is parked for an extended period of time, the battery charge level will become low. Extended periods of time at a low state of charge will shorten battery life. To maintain the battery state of charge, drive your vehicle for more than 30 minutes at least once every three months. Extreme high temperatures can affect the battery life. You can minimise the effects by parking the vehicle in the shade during the summer.

The 12V battery is recharged by the high voltage battery but only if the car is used!

Addendum: Quote is from p400 of the online MY24 manual

Yes, I'm aware of that, that's why I said "By implication". If the 12V battery has a much shorter charged life than the HV battery, surely that would be the limiting factor that would be quoted in the handbook? There'd be little point in specifying "30 minutes every three months" if the 12V battery had a resting discharge rate such that the car couldn't actually lie idle for that long.

[Whiteshark]

I took it to be able to leave the car for 3 months unused.  This has all been discussed on here before, which meant I followed that advice before leaving my wife’s Jazz unused for 7  weeks in April/May this year, whilst in Australia. However I made sure the battery was fully charged using my CTEK, beforehand, without disconnecting the battery.
On return, as with all our Honda’s , no problems whatsoever. I do think it is important to make sure the 12v battery is fully charged though before leaving it for extended periods.

[John Ratsey]

How many weeks does the delivery boat trip from Japan take (I think it's several weeks)? I doubt that anyone either disconnects the 12V batteries or tops them up during those trips. Do they even remove the keys and lock each vehicle?

The HR-V had a known bug of the 12V system sometimes not shutting down properly for which Honda issued a software update that is only applied after a vehicle has had a problem (to minimise paying dealers to apply the update).

[Kremmen]

I think some fuses are removed to help protect the battery and the dealer inserts them when required.

I remember a customer returning to a dealer when I was in the showroom and they said a fuse had been missed.

[plasma]

Ditto on the double lock.

The same here. Always (and I mean ALWAYS) on the double lock plus switch off the key fob.

Can you explain what you mean by double lock please.


Plasma.

[Lord Voltermore]

I once left the car unused for over 2 months without problem with the 12v battery.   But I  did take the precaution of plugging in a solar powered trickle charger  . (It plugs into the OBD11 port)   This may have helped, although the rate of charge in January and February, with short daylight hours, could not have been much . I think I made sure both keys were disabled, but nothing else.   But the car did have regular use prior to that so was probably well charged.

A solar powered charger might be a solution for those who use their car infrequently and no access to mains power for a smart charger.    I used one of these - but there are more powerful versions available.

It can plug in to the OBD socket, but this is a bit of a Faff to reach on the Jazz if used regularly. But it would be easy enough to fit ring terminals to the battery in place of the supplied crocodile clips, with the connecting plug inside the car,saving the need to lift the bonnet.

https://www.amazon.co.uk/Powered-Battery-Charger-Caravan-Package/dp/B07P7C6QLD/ref=asc_df_B07P7C6QLD/?tag=googshopuk-21&linkCode=df0&hvadid=232037057466&hvpos=&hvnetw=g&hvrand=7305217838032026590&hvpone=&hvptwo=&hvqmt

It may seem a lot of messing about  but dont let it put you off buying  a Honda or a Hybrid.   There are numerous reports on line  of other makes of  conventional cars  flattening large 12v batteries in as little as 2 weeks.Modern cars have  so many electronics tdrawing power  24/7  , transmitting and receiving signals to keys, telephones ,gps  etc  its difficult to avoid the problem entirely.  Especially if the car gets little use.