Lets talk battery chargers
 

My D3 does not get much use for weeks on end, and then I'll do a 400 mile return journey.

For example in the last 5 weeks my D3 has been used almost daily, yet it has covered just 55 miles.

As a result I think that the car is consuming more power than I am putting back in, that coupled with the slight battery drain issue is leading to less power.

After 5 weeks I am getting up in the morning to find that the BCM has turned a lot of stuff off, so keyless entry is disabled and the light in the door is not flashing so I need to use the unlock button on the key to open the car. Once inside I can start the car with the start button, and the battery monitor is down at 15% or so. After driving to work, its up at about 80%, but I switch off at that point. Same at the end of the day, except I usually leave the engine running for a bit to get the battery meter to 100%

We all know the battery meter is just measuring voltage, and I confirmed that with the meter on 100% the battery is still receiving current from the alternator, which once charged the BCM stops.

So looking for a charger really, not to expensive but something I could use say weekly to topup the battery. I've tried a big solar one directly on the battery but I don't think it was doing much as they tend to be to help maintain a well charged battery.

Battery is fine, its 20 months old and never been run fully flat and always starts the car without issue. The car will be fine for several weeks after the long run, before getting back to where I am now.

C-Tek chargers...

+1

CTEK MXS 5.0 can maintain 110Ah like ours.
Not much change from £60 notes though.

Check out this one available at Lidl from tomorrow. http://www.lidl.co.uk/en/our-offers-...&id=27134&ar=3

I have LCD version of the same charger https://www.youtube.com/watch?v=NO9MWevR1yk (not me in the video ) and it's been great to top up or keep charged battery but being 3.8A it takes long time to charge from flat. It takes probably around 20 hrs to go from 20% to 80%. At 80% it cuts current to 0.8A just like C-Tek chargers so it takes another 24 or so hours to get to 98% so you are looking at 2 days or more to go from flat to fully charged.

manny this could also be caused by a faulty BCM as that is exactly the behaviour exhibited when they start to go a bit funny. Suggest you plug vagcom in and recode the battery by adding 1 to the previous coding and digits and then the BCM thinks you have fitted a new battery and you don't seem to get the same issue again for ages if that's what it is. Worth a try anyway. +++

I am now more than sure the reason for the overnight battery issue is the boot electrics. Last night I needed to access the boot after driving home from work, and this morning the battery was fine and just under 100% charged on the meter. Same this evening, 100% charged after sitting in the car park all day.

So what on earth can cause issues with the boot electrics. I know that if I close it manually I can sometimes press down on the supposedly locked boot and here another click like something was not engaged properly. My electric boot is missing the little spring so it does not close itself without opening up again. I dont think its the boot light as that goes off after a short while if you leave the boot open anyway.

I've still decided to get a charger, and may go for the ctek one mentioned, at 11 years old she is developing electrical gremlins.

Well the car did it again, so I've followed Neil's advise and recoded the battery module by incrementing the serial number one.

Lets see what happens now.

At least next weekend I'll be doing 400 miles and putting plenty of charge back in.

My understanding is you need to fully charge the battery then recode the BCM or does it not matter?

Well coding the battery made no difference, after 24 hours battery back down at 15% and this is despite leaving the engine running outside for 1/2 hour and then going on a 15 minute drive as well. The tell tale sign is that the alarm light is no longer flashing in the door and the keyless is dead.

I've been all round the car and opened/closed everything that can be, that has been known to sort it before. it used to happen once in a blue moon, but its a bit of an issue these last two weeks.

I must have one heck of a current draw, but everything is working and nothing seems untoward. For now I've left the car on the level outside, with the parking brake off just in case I need to push it out of the way due to flat battery to get the tired old A6 out.

Try taking the battery off and charging it over night or as long as possible, once fully charged then try to recode the BCM, iirc it gets its new parameters from the new battery itself, either that or invest in a DC ammeter and let the car go to sleep with access to the fuses without disturbing anything and start pulling them till you find what circuit it's on.