12V Battery after long stand still

[peterhuckle]

On my old Fiat Panda I just used to disconnect the battery when leaving it for a long time and reconnect when I returned.  The battery seemed to be able to retain a large enough charge to start the car even after over a year.  Would that be possible on the 12 volt battery of the Jazz to prevent drain from the sleeping electronics?

[Bristol_Crosstar]

On my old Fiat Panda I just used to disconnect the battery when leaving it for a long time and reconnect when I returned.  The battery seemed to be able to retain a large enough charge to start the car even after over a year.  Would that be possible on the 12 volt battery of the Jazz to prevent drain from the sleeping electronics?

If there was no power to the electronics the system would probably forget all your settings and effectively do a 'factory reset' when the battery was reconnected so probably not a good idea

[Lord Voltermore]

On my old Fiat Panda I just used to disconnect the battery when leaving it for a long time and reconnect when I returned.  The battery seemed to be able to retain a large enough charge to start the car even after over a year.  Would that be possible on the 12 volt battery of the Jazz to prevent drain from the sleeping electronics?

Disconnecting is not a good idea. If the 12v battery is discharging in less than 3 months there may be some DIY solutions.   Regular topping using a mains smart charger.   Or if the car is outdoors  connecting a solar panel charger may give a trickle charge that exceeds ,or delays its natural parasitic electronics  discharge.
 
If you regularly leave the car unused for 1-2 months and have no mains power for a smart charger  it might be possible to temporarily connect a remotely located 12v battery to the cars 12v battery  wired in parallel. This would give 12v but a greater reserve capacity.  I am not an expert so there may be objections to this. 

I carry a portable battery pack   jump starter in the car   The battery is only about the size of a paperback book. Its said to be able to start a conventional car with starter motor so my hope is in an emergency it will easily power up the  12v Jazz electronics long enough for the HV battery to start the car.   But I have never yet needed to use it so cant guarantee it will work. 
Bear in mind that most new cars, including conventional ICE engine ones with large 12v batteries   ,have electronics running 24/7 ,and can flatten their batteries in a matter of weeks or days if they dont get regular long journeys. 

 The biggest obstacle to not using the car for long periods is not the 12v battery  but  the High Voltage battery. Unless the car is driven for at least 30 minutes every 3 months, to put the HV battery through some discharge/recharge cycles, the HV battery can be permanently damaged.  And very expensive to replace.    A 12 Volt battery can also be permanently damaged if allowed to fully discharge but relatively cheap and easy to replace. 
A HV battery charger, costing £1000,s ,only viable for professional garages ,might be able to deal with cars in Long term shortage, but this is beyond  the  ability  of domestic smart chargers etc. 

[Jazzik]

Opened the garage this morning for the first time in months. The Jazz has been parked there since February 20.
Due to (medical) circumstances, the car was not used for 71 days (10 weeks, 2½ months).

When I park the car I always turn off the audio, use "dead" (double) lock" and switch off the key fob.

The HV battery should be safe because it has not been used for less than the 3 months Honda warns for. But how did that little 12 volt battery hold up?
With fingers (also toes and eyes) crossed I pressed the unlock button on the key.
Flashing, mirrors unfolding and everything seems ok.
Foot on the brake, finger on power button... and I see 9 (nine!!?) bars on the left.... HV battery almost full? After such a long time? Indeed!
I have no idea what the voltage of the 12 volt battery was, but it was certainly enough to start the car.

After a drive of about 45 minutes, the Jazz was parked again with peace of mind.

[Lord Voltermore]

Welcome back Jazzik  .I'd missed you. 

[coldstart]

...
Due to (medical) circumstances, the car was not used for 71 days (10 weeks, 2½ months).
...
With fingers (also toes and eyes) crossed I pressed the unlock button on the key.
Flashing, mirrors unfolding and everything seems ok.

Thank you for the positive feedback on this topic!

And a hearty welcome back! I hope you are well again!

[John Ratsey]

With fingers (also toes and eyes) crossed I pressed the unlock button on the key.
Flashing, mirrors unfolding and everything seems ok.
Foot on the brake, finger on power button... and I see 9 (nine!!?) bars on the left.... HV battery almost full?

Lithium batteries have a very low self discharge rate. New ones are shipped part charged and can sit on shelves for years without dying. In addition, the HV battery in the Honda is disconnected when the vehicle is powered down so there's no risk of any parasitic power drain discharging the HV battery. It's the 12V battery that gets drained.

[Botak]

The experience of Jazzik is a good cause for me, as the topic-starter, to share our last experience with a long stand still during winter (every time about 2 and a half months). I have already shared the data of the battery-charge of our Jazz in the first 2 years. I can add the figures of this year. For clarity, I give the data of the 3 years together:
2022: departure 12,8V return: 11,9V
2023: departure 12,6 V return:11,6V
2024: departure 12,5V return: 11,7V
Even considering the soft Dutch winters (certainly in a garage), the small 12V battery is quite sturdy. The charge of the battery is deteriorating, but very slowly. And did I first wonder if the battery could cope with one long standstill of 2 and a half months (and was already searching for a fitting EFB-battery for replacement) now my only concern is that I can get exactly the same battery when I have to change the battery in a couple of years.

[Kremmen]

From previous posts it seems that the charge level of the 12v battery when you leave it may have a bearing on how long it will last with some charge