Protecting 12v Battery over Christmas & New Year

[RuthieB]

This may have been mentioned elsewhere on the forum regarding “booster packs” but what do folks recommend using?
There appears to be many powerful (and expensive) packs out there for ICE vehicles with conventional starter motors but am I correct in my understanding that such packs are overkill in restarting a flat battery Jazz which really only needs the 12V battery/ low current starting circuits initiating the High voltage battery to engage with the electric motor?.

What do folks recommend aligned to personal experience please?

Thanks in advance

[Lord Voltermore]

I prefer not to rely on a rescue service if possible. I have a multiple  approach.
1) Try to ensure the  car gets regular  journeys ,of long enough duration to recharge the 12v battery.
2) If it only gets short trips I would use a mains powered   smart maintenance/trickle charger to keep it topped up.
3) If left for long periods  unattended  I would attach a solar charger.

For emergencies -
1) I carry a small 'power bank' type jump starter in the car. .  Its only 150mmx75mmx20 mm  (6"x3"x3/4") with a small set of crocodile clips able to give a peak of 400 amps at 12v (for a very short length of time probably) .  These claim to be able to jump start a conventional ICE .    Hybrids actually start their engine using the HV battery. The small 12v battery only needs to be able to power up the cars computer system which carry out tests in a few milliseconds  before throwing a heavy duty solenoid switch to connect the HV battery which starts the engine.   I have read that it only needs about 30 amps to do this so the little pack should be able to do this easily.  But TBH I have never needed to use it so cannot vouch for whether it will work.     One downside is that  if you get to the situation of needing a jump start the 12v battery may already have suffered some damage/deterioration . But thats true however powerful and sophisticated your jump starter.  Prevention is better than cure. 
You do need remember to keep it topped up  about once every 3 months (Xmas,wifes birthday, my birthday, wedding anniversary works out  well for me  ) Easy to charge using a simple 5v usb lead, maybe even from the car.   Also has uses as a torch, or portable 5v power bank for charging phones  etc.

 2)  I also still  carry a pair of conventional jump leads. I might be able to cadge a jump start from another car. However I wouldnt offer to jump start someone elses ICE car with my Mk4.   It might damage the small  battery or delicate electronics.   (I might offer  to help by using my little power bank thingie, to see if it works  )

3) if all else fails  ,call for assistance. 

In my opinion (but not yet put to the test  )  a small power bank will be sufficient  for a hybrid.  But a more powerful alternative may be better if  you might occasionally wish to start a conventional ICE car.

I have been concerned for years how the AA (and probably also the RAC) have evolved from 'clubs' offering good value and  lots of information to members  into organisations  that simply want to flog you stuff . Germanies ADAC and Austria's OAMTC seem much better in this respect.

 . I assume the attending van will still be fully equipped with tools ,diagnostic equipment, universal spare wheels etc, but do they actually carry a variety of replacement batteries ? .Or will they delay attendance while they obtain a battery they will then pressurise you into buying? 
 
I can understand that  it may be very convenient getting your battery replaced  by them, and they would not be very happy attending a second time for the same reason if you failed to replace it yourself.  But I'd rather shop round  myself for the best battery and best price.       

[aphybrid]

My carry 'jump' starter https://www.mobilesolarchargers.co.uk/shop/details/overland-waterproof-car-jump-starter.

Used in anger twice on my wifes ford fiesta st line x after being left in garage for a few weeks whils on holiday.

[Geoff_W]

Thank you all for your helpful replies. I do have one of those little voltmeters and it always shows an initial charging rate of 14.6V, falling to about 12.2V when charged. I always 'double lock' and switch off the remote when going away, so hopefully I should be OK, especially as I have a relatively new battery.

You need to see it drop to substantially less than 14.6 volts with the power system on so that you can be sure that it is almost fully charged.

I asked Chat GPT to search around for some measurements on the power off current for the Jazz (and the Yarris too).  It replied that several users have measured the Jazz at about 25mA while the workshop manual quotes a worst case of 50mA.

Now 50 mA for 30 days works out at 36 amp hours which is roughly the battery capacity so that would seem marginal for you in the worst case.  Typically though you should be fine.

Battery capacities are usually quoted at the 20 hour discharge rate and the one month discharge rate will almost certainly result in more  capacity - just how much more I don't know.

Thanks for this info. I was quite shocked at your calculation of 36Ah, but you are absolutely correct. As you say, it's a bit marginal. I have an old Gunson 12v Automatic Battery Charger which I used on ICE vehicles. Would this be suitable for use on a hybrid?

[NetworkMan]

I don't think it is the hybrid that is the issue; it is the type of battery.  If it is not a traditional lead acid battery then your charger may not be suitable.

It seems to me that in the hybrid car you have a pretty good petrol powered battery charger though rather expensive to run compared with a mains powered one.  If you turn on the power system you can wait until the voltage on your plug-in voltmeter drops from about 14.5 to around 13.3 or whatever - this should be a rapid transition - and call it job done.  If you can use the car a bit after that so much the better so long as it is less than a day or two before you go away.  Of course, just using the car is as good as leaving it on the drive with the power system on.

The 50mA and one month was not a surprise to me since my 2014 Mazda MX-5 NC also draws about 50 mA and can deplete the battery in a few weeks.  That car suffers from a less good charging system which just stabilises the voltage at 14.1 and therefore takes a long time to recharge after a start. Short journeys are a problem.

Remember to switch off the remote keys and lock the car so as to put it in the low power state.

Just had another thought.  Has anyone on here thought of just disconnecting the battery? Pretty sure you can still lock the car.  I would happily do it on my old MX-5 but not sure how much of a pain it would be resetting all the systems on the Jazz which would presumably go into some undefined state.

[ahavoja]

Has anyone on here thought of just disconnecting the battery? Pretty sure you can still lock the car.

I'm wondering how would this work...
1. Unlock the car.
2. Open the hood.
3. Disconnect the battery.
4. Close the hood.
5. Try to lock the car... But it shouldn't lock as the car doesn't get electricity from anywhere. But maybe you could use the lock tabs near the interior door handles to lock all other three doors from inside?
6. Exit the car and lock the driver's door using the mechanical key.

This could help protect the 12V battery but it would also worsen the protection against thieves as the security system alarm of the car wouldn't work without electricity.

[Lord Voltermore]

I used  to disconnect the battery on a 2010 Corsa when left for long periods.  I'd lift the bonnet,,then lock the car BEFORE  disconnecting the battery and dropping the bonnet. On return I'd open the car with the manual key blade,. The after-market  alarm would sound when I (or a thief) reconnected the battery .

It does mean the car is left with no audible alarm  (if it has one)   but  still has its immobiliser function that uses  proximity chip/signals from the car key.  Depends how likely you think it is that someone will break into the car. In which case any damage will already have been done, even if  the thief then ran away quickly. 
 
I can remember a time when false alarms were so common they were widely ignored .You would sometimes hear starlings and other song birds imitating a car alarm. 

But insurers may object  . Also with its advanced electronics I  would be wary of disconnecting /reconnecting  the battery on a mk4  . (although if the battery went completely flat  it might have a similar consequences anyway  )   

[NetworkMan]

Almost exactly what I thought when I posted the idea.  You also still have the deterrent effect - in both cases the damage is done before the alarm is set off, or not set off.

[Kremmen]

From what I've been told, years ago, car 12v batteries have 2 stages of charge

The first charge is performed in the factory and is designed to allow garage forecourt storage over long periods. This is how those on garage shelves don't go flat as long as there is no drain by anything connected

Once in the car the alternator takes over and performs the second level charge

If, as happened to me, you (she) leave lights on and the battery fully drains both second and first level charge then it's more than likely the battery is dead, as, from what I was told, the alternator can charge the second stage but does not perform the first stage charge and without that the battery will auto drain in a matter of hours

[5thcivic]

I do wonder how long those cars stand on the forecourt, and whether garages go around doing a super charge from a big trolley battery every month or so. Car battery on a shop shelf with nothing connected is a different situation to cars locked maybe for weeks until sold? Of if you come in and say I'm interested in the red one do they sit you down for a chat while a service guy quickly runs round for a charge to make sure it starts first time?

[Lord Voltermore]

I do wonder how long those cars stand on the forecourt, and whether garages go around doing a super charge from a big trolley battery every month or so. Car battery on a shop shelf with nothing connected is a different situation to cars locked maybe for weeks until sold? Of if you come in and say I'm interested in the red one do they sit you down for a chat while a service guy quickly runs round for a charge to make sure it starts first time?

My local VW dealership  (sorry - I had a quick look    ) has a specialised 12v charging circuit  built to the showroom floor (not just 240 volt sockets for separate chargers) )  On my visit all the ICE cars were plugged into their adjacent 12v sockets. Quite discrete but I did notice   .   I dont know  if this is 24/7 or just for a periodic top up. I think most dealerships periodically put the showroom  cars on a trickle charger perhaps overnight.

 But I doubt the same periodic battery care is taken for their stocks of new and use cars that may stand idle for long periods before sale. They normally have a large portable jump starter unit , but thats too little too late.