What about a flat battery

[Borat]

I am worried that when we go away for a few weeks, the battery may run down on our new Golf Alltrack (though on our '04 Bora it has not happened so far) in which case - what happens? Can we get into the car to at least put it on the charger? Is it best to leave it unlocked in the shed, or even on a charger? Seems like with so much electronica letting it go fully flat could be tricky/expensive/serious. Any thoughts or experiences? Cheers.

[DV52]

I am worried that when we go away for a few weeks, the battery may run down on our new Golf Alltrack (though on our '04 Bora it has not happened so far) in which case - what happens? Can we get into the car to at least put it on the charger? Is it best to leave it unlocked in the shed, or even on a charger? Seems like with so much electronica letting it go fully flat could be tricky/expensive/serious. Any thoughts or experiences? Cheers.

Borat: very excellent questions indeed- well worth the asking!!

The important thing (IMO) to note is that the role of the humble car battery has certainly changed over the years and in the mk7, it's become more integrated into the car's electronics. I'm assuming that your alltrack is fitted with Start Stop which means that it most likely will have a Battery Monitor module (which VW calls "J387"). If you look at the negative battery clamp, you should see J387 as per my picture below:



Don't worry about the yellow stuff- it's an anti-frosting spray that dealers use.

So, the role of J387 is to constantly provide data about the battery's health back to various control modules in the car. When most of these modules are required to make a decision about the car's voltage-rail, it's a calculated measurement that is used -it's not the actual terminal voltage @ the battery. For example, when the car is stopped, there is a decision made by the Start Stop function as to whether there is sufficient energy in the battery to crank the engine - if there isn't sufficient battery capacity, SS won't switch-off the engine. A calculated battery voltage is used in this decision.

J387 in instrumental in keeping an accurate database of every ampere of electrical current that has ever been put into the battery (by the alternator), or taken out of the battery. So it's very important not to by-pass this module if for example, you are charging the battery.

If you have J387 installed- don't ever place the negative lead from a charger (or a jump battery) directly onto the negative battery terminal in the car - If you do this you will by-pass J387 and the charging current won't be registered into the battery history table in the car - this will make the calculation of "system" voltage incorrect.

Always connect the negative charger lead to the body of the car, or better still connect the lead to the special clamp provided for this purpose - see below



So if the battery does become flat and you re-charge the battery (in the correct method as above), the modules in the car will get cranky and you should expect a number of error codes. But don't worry - just drive the car for a while and all the alarms should clear by themselves.

Don

[Borat]

Thanks DV52. I just checked and the battery terminal has a cover plate with pictures indicating the correct charging point, which is not the battery terminal but an auxiliary bracket, as you noted. I'd send a picture but it's dark now (and not sure I have the technical skill!). As a PS, what happened to the old radio/infotainment not working after the battery is disconnected or flattened? Was that always a myth, or is it still an issue today? Seemed to be a non-issue when our '04 Bora got a new battery, happily.

[peekay34]

Just buy a trickle charger that's what I do when I go away for extended time. less than a $100

[timsimms]

A few weeks without a start is something I don't think you need to worry about. I just had a month holiday, car started no problem when I got back.

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[Idle]

Just make sure the car is locked, everything turned off — and don't leave the key in it.
Should then be OK for a month or so.

[stefcio007]

Ford's have a battery monitoring system almost identical to the one above too so they probably work the same way. (I don't have a start stop system)

I just came back from a two week holiday and the car battery dropped from 80%
(the system stops charging by design at 80% to extend battery lifetime)
to 54% (checked data stored in the car's monitoring system).
My car has an aftermarket radio which probably saps more standby power than the stock unit.
To preserve the battery, before starting I just put a charger on it for a few hours.
There is no option for me to have a charger on the car while I'm away but I would do that if possible.

[brad]

I've gone away for 8 weeks and car has started without issues.

They use less "standby" power when locked. Store the key in a faraday cage (tin can) so that it isn't polling the vehicle.