Non-boaty car battery question.

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FairweatherDave

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Daughter coming back from her travels and getting her car back on the road. A small petrol engined VW Fox with a 550A battery, 60Ah. Battery less than a year old with a 5 yr warranty but flat as a pancake. Read less than 4volts on the multimeter.... It started the car a month ago. Anyhow the MOT is tomorrow and I need to drive it there and back. IF the charger fails to do a reconditioning charge on the Fox battery could I temporarily put in a battery from my son's petrol Yaris. This is a smaller battery, 40 Ah 370A .Or is there a problem? Thanks for any knowledgeable answers, I only go so far on electrics.
(Longer term there may be an issue with the proper battery for the Fox and that is something she can sort out with access to all the warranty paperwork, I'll have done my bit if I get it through the MOT and out of the front garden:)).
 
Smaller battery will either have the CCA to start the Fox or it won’t. If it does, it will be fine.
 
If these are modern cars, less than say 10 years old, you may get warnings and errors flagged up if you change the battery.
Leaving the battery to go flat, not using the car for a month is not a warranty issue, it's self inflicted.
Is it stop-start?
Modern cars complicate everything, they are not all the same, so reading the manual may be a start.
Some cars it's important to charge the battery and/or jump start from the dedicated connections under the bonnet, not direct to the battery.
 
Fox is 9 years old, yaris very old.......
The warranty is only significant because it stops me buying a new battery. Yes cars like being used and batteries like being kept fully charged.
Not sure what you mean by "Is it stop start"?
 
FairweatherDave said:
Not sure what you mean by "Is it stop start"?
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Does the car irritatingly stop the engine automatically when you put it in neutral, and restart it slightly too slowly when the traffic-light goes green, in order to eke out a fraction more fuel-efficiency in government tests? ;)

If so, it might have a more advanced battery system to cope with all the starts.

Pete
 
The yaris battery will do temporary if you need it, but make sure it is properly clamped when going to mot. The battery may charge up ok, especially since it is not that old. Modern cars will drain the battery after a few weeks, you could buy a solar panel that plugs into cigarette socket if you have to leave car for extended period.
 
FairweatherDave said:
Daughter coming back from her travels and getting her car back on the road. A small petrol engined VW Fox with a 550A battery, 60Ah. Battery less than a year old with a 5 yr warranty but flat as a pancake. Read less than 4volts on the multimeter.... It started the car a month ago. Anyhow the MOT is tomorrow and I need to drive it there and back. IF the charger fails to do a reconditioning charge on the Fox battery could I temporarily put in a battery from my son's petrol Yaris. This is a smaller battery, 40 Ah 370A .Or is there a problem? Thanks for any knowledgeable answers, I only go so far on electrics.
(Longer term there may be an issue with the proper battery for the Fox and that is something she can sort out with access to all the warranty paperwork, I'll have done my bit if I get it through the MOT and out of the front garden:)).
Click to expand...

With the cars you describe, stick it on and try, if it starts (which it should) it will be fine. Make sure (as suggested) that the battery is secure or it will fail the MOT.

Unless something was left on, i would not expect the battery on that car to go flat in a month.
 
Thanks Pete. I was thinking it was maybe some kind of intermittent fault :)
They are both modern cars really, but the Fox battery access is a pain in the ****, Yais is a doddle.
Hoping the warrantied battery will make a full recovery, but I am mystified how it can go from starting the car fine to reading such a low voltage in what seems like three weeks. I'm sure no lights were left on or whatever.
And thanks Paul, that is reassuring.
 
Have you been regularly starting the car each month? But then turning off when started ie not leaving the engine running long enough to put back in what starting has just taken out as doing this a few times will gradually flatten the battery, to a point where it will self discharge.
Another could be something has been left on eg boot interior light as this cannot be seen. This will easily flatten the battery
 
Rocksteadee said:
Have you been regularly starting the car each month? But then turning off when started ie not leaving the engine running long enough to put back in what starting has just taken out as doing this a few times will gradually flatten the battery, to a point where it will self discharge.
Another could be something has been left on eg boot interior light as this cannot be seen. This will easily flatten the battery
Click to expand...

Yes, that is all possible. But she's only been away 3.5 months total. Anyhow get the car up and running and see how it goes. Most important thing is I remembered to leave the hand brake off (after I had left it on for a few days and it had started to seize).
 
So many cars have significant drain from alarms etc, badly designed ecus, remote unlocking and other electronics, they really are not intended to be left unused for long periods.
Starting a car and letting it run for a few minutes can be an own goal with some cars, it wakes up the computers which then draw more current for the next few days!
These days, for long term storage, you need to either disconnect the battery or use a trickle charger.
 
lw395 said:
So many cars have significant drain from alarms etc, badly designed ecus, remote unlocking and other electronics, they really are not intended to be left unused for long periods.
Starting a car and letting it run for a few minutes can be an own goal with some cars, it wakes up the computers which then draw more current for the next few days!
These days, for long term storage, you need to either disconnect the battery or use a trickle charger.
Click to expand...

Unless you know for certain that this will not cause damage, don’t. Some cars it can kill the ECU (Engine control unit) if longer than momentarily.
A trickle charger is the best option
 
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Rocksteadee said:
Unless you know for certain that this will not cause damage, don’t. Some cars it can kill the ECU (Engine control unit) if longer than momentarily.
A trickle charger is the best option
Click to expand...

It's often not recommended, but lots of people report disconnecting car bateries when the vehicle is not in use.
Do you know of any verified cases of an ECU being damaged by removing power? Which vehicles?
A charger is not always practical.
The trouble with disconnecting the battery is that some vehicles need power to open the boot, where the battery is...
 
lw395 said:
It's often not recommended, but lots of people report disconnecting car bateries when the vehicle is not in use.
Do you know of any verified cases of an ECU being damaged by removing power? Which vehicles?


Yes. Peugeots are notorious for damaging BCM which will need replaced or/and initialised. Some cars will loose immobilizer. It's not recommended, you might get away with it, but it's not worth the risk, it could cost £100s to fix.
QUOTE]
Click to expand...
 
lw395 said:
It's often not recommended, but lots of people report disconnecting car bateries when the vehicle is not in use.
Do you know of any verified cases of an ECU being damaged by removing power? Which vehicles?
A charger is not always practical.
The trouble with disconnecting the battery is that some vehicles need power to open the boot, where the battery is...
Click to expand...

I don’t know. My dad used to have a garage and one of the mechanics used a plug in cigarette charger to maintain voltage when battery disconnected
 
What do they do at Halfords when they change a battery (re. maintaining voltage)? Just curious. Bit late now for me as the battery has been out charging all day, still in the bulk absorption phase. But I might interupt and fit the battery soon and finish the charging in situ with the hope it will start at 7.30 am. Tried charging in situ last night but for some reason it didn't work. (Lightweight extension cable maybe or poor contact). Access rather awkward for a jump start.)
 
Rocksteadee said:
I don’t know. My dad used to have a garage and one of the mechanics used a plug in cigarette charger to maintain voltage when battery disconnected
Click to expand...

I left my DS with a smart charger maintaining the battery. Unfortunately one cell died and the charger, seeing only a flat battery, kept pumping 3.7A through it, completely drying out the dud cell and blowing off the cover plates to the cells. Luckily no worse than that - the car is in a very well ventilated place so the gases released will have dissipated at once, but a spark inside a batery pressurised with hydrogen-oxygen mix could have been fun.
 
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