Battery drain...

[Tiprat]

This summer we went away left the car (A4 2lt TDI Conv) parked for 15 days and came back to a flat battery, ok so I guessed it was just a simple thing like, new battery did a drop test on the one in the car and it was just in the ok range, easy fix as I had a good spare.
But no it came back when we went away for a week.
So started looking through the forums, for answers and help. And monitored the voltage drop over night, most nights it would drop 0.6-0.8v.
There are no lights coming on or off either on the dash, hazard switch, boot, rear lights ect. I've swapped the alternator for another one, I've took the plug and positive leads off the alternator. Now I've even bought a brand new battery, but still I'm getting a drop over night. It's been in the garage, and on a diagnostic with no codes showing. I've had a look for blocked drains in the battery area all is dry. The carpets appear dry, there's no misting up inside over night. So now I'm at a loss as what to look for, so any help would be appreciated, I'm based in Worsley and every one I've asked can't suggest an auto electrician even the garage. So I'm stuck at present and with winter coming I'd rather trust the car to start after a night shift rather than risk a flat battery from it draining away.

 

[Sp3no82]

you need to preform a parasitic battery drain test with a multimeter. Basically shut the car down but keep a door open but flick the latch on the door so it appears closed and turn of interior sensors. Once the car has gone to sleep its time to test all of the fuses to see if any current is being drawn when the car is off and asleep essentially.

 

[Tiprat]

Thank you for your reply but I'm unsure how to do a "parasitic test".
I have a basic (cheap) multimeter, but I'm not skilled in the use of it. I understand what your saying but not how to do it, ie settings on meter. I'm guessing that I leave drivers door open press sensor switch in drivers door and lock it with the key,
Then which fuses do I remove, I don't want to remove a wrong one and end up triggering a fault, or dash light to come up. And what do I look for on the screen of the multimeter?
Thanks.

 

[p-rossi]

+1 on Sp3's comments. I still have a battery drain issue due to RNSE causing the CAN Infotainment BUS to wake up some modules. I've posted all about in on here. Anyway, you could get a multimeter with a current clamp to monitor the draw from the battery or just put a normal meter in line with the negative lead (just make sure you don't turn over the lump). My car took around 20mins for all the modules to go to sleep. Once it had, it was drawing about 2.5A so the battery went from full charge voltage to about 2V overnight. It was intermittent so I didn't see it immediately.

If it's a continuous drain, then you'll see it on the meter straight away so you can start pulling fuses to see what's causing the drain. If your multimeter will measure down to 0.1mV, then you can monitor the current draw without removing the fuses. There is a chart online that tells you how much current is going through a fuse based on the voltage drop across the fuse - if you can't find it, let me know & I'll dig out what I have. Otherwise, start pulling fuses 1 at at time & watch for the current draw to drop. If the drain is intermittent, (ie, not a cabling short or a light staying on) then you might not see it unless you can record the draw on a data capture multimeter but I know not many folk have them just lying around.

You could always test the relays in case one is sticking on (under the knee board & inside the ECU housing).

When you changed the alternator, did you change the whole unit as it could be a leaking regulator or diodes?

 

[Tiprat]

I changed the whole alternator, as for the RSNE I have the concert radio rather than the mmi would that make a difference.

 

[p-rossi]

If it's just a basic multimeter then the current setting may only be good for 300mA or so. If the current draw is high enough, then it could pop the fuse in your multimeter. It'll depend on how long it takes for your battery to drop by 0.6-0.8V, but I'm guessing your drain is not more than an amp or so(?). Best not to guess & work it out before you put you meter on there. Just make sure you're using the DC Amps setting & remember to select the right socket on the meter. I'm not meaning to be rude, TipRat, but I'd guess by your reply that you might want to have someone assist you with the multimeter - don't want you frying anything or zapping yourself.

It doesn't matter that whether RNSE or Concert - it's just another device that draws current & it just happens to be RNSE that's causing my drain issue. If you're pulling fuses out, then you'll be taking power away from the radio anyway along with all the other fuses. What I wasn't sure about myself, is whether other modules in the car 'know' that a module has just had its power removed due to CAN Bus links or other connectivity, causing the remaining modules to wake up & draw more current. If it does happen like this, then the parasitic current draw (the unintentional current draw from the battery with everything off, key out,....) will be masked. Pulling all the fuses out from the fuse panel at the end of the dashboard, will kill power to the devices they feed but if you have a wiring issue (eg, water between contacts or a bad earth, etc) then current may still be flowing.

 

[p-rossi]

....and while you're working out what's causing it, you might want to think about disconnecting the battery when you leave the car overnight or at work, if you can. I did this until I worked out what fuse to pull as I'd killed 2 batteries because they wouldn't hold a charge after all the draining.

 

[Tiprat]

As always guys thank you for your replies, I shall start looking again once it's dry!!!
Just out of interest where are the earthing points on a convertible and I shall clean them up too.

 

[Mike B]

Perhaps it might be relevant to say that we spent a long time wondering where the battery charge was draining on a TT Roadster until noticing a leak in the rear window just over the convenience module .Had to get a replacement

 

[Tiprat]

Is this the module that people call the CCM module under the passenger seat? I've seen some threads mentioning that, so when it stops raining il see if the insulation under the carpet is wet.