Drained battery - my story

[saksager]

Hi all

I hope this will come in handy for others experiencing drained battery. I suppose the error I found is not the most likely to occur, but still I hope you can use my experience for something. I search a lot for a solution, and during my search I came across several people, who had talked to a dealer about a battery drain issue, and some of them had been told, that a current drain of 0.5A is ok. Well, mildly put, that is just not true, and just a way to sell a new battery. For a 74Ah battery like mine, it will drain the battery completely in 6 days if not charged. That means that the dealer says it is ok to park the car at the airport, and then returning from vacation and finding the car totally flat 0.5A is at least a factor of 10 wrong - 0.05A or 50mA will allow you to park your car for 60days, which seems more right...

So here is my story.

A couple of weeks ago, my vRS (petrol) began to struggle at engine start, but only just noticeable. During the last week or so, it really struggled, and I began to look for a new battery (5 years old now), until I came to think of that something might have drained the battery. So I attached an ammeter in series with the negative pole on the battery to watch the battery drain over time.

Immediately after locking the doors, the current is approx. 2A and quickly dropping to 1.4A or so. Then it dropped to 0.7A, but then it started fluctuating between 0.7A and 1.4A. Then I started pulling out all fuses in the cabin fuse box, and that did not help. Then I sat in the cabin for some time and wondered... I had already checked for lights, which are often known to drain batteries, but they were all ok (and I had already taken the fuse out). After some minutes, I heard a clicking sound, and found that the clicking sound had the same pattern as the fluctuating current. I then took out the glove compartment, and found the source - the box for the central locking. I took the box out, and opened it. On the PCB I could see some corrosion/deposits, and I thought: "Well, since it does not work now, it can't get any worse...", so I cleaned the PCB in Isopropyl alcohol and dried it with a hair dryer (not mine ) and connected the module again. I then closed the door, and waited - nothing, just silence

I have now tried to log the current drain for an extended period five times, and every time the current drops to 20-30mA after approx 7 minutes - and stays at that level.

Now, I just have to replace the battery, since it is dead after being too drained (it read 5V or so), so please take my advice and put on a charger while you are doing the diagnostics - it just cost me £100 or so for a new battery.

My recommendation for finding the current leak are as follows, and remember to ALWAYS wait 10 minutes before you measure to ensure that control modules are in hibernation mode:

• 
  [1] Put on a charger.
  [2] Use an ammeter to measure the current drain. You can either use one in series withe the battery or a clamp type. One attached in series is more precise, but remember NOT to turn the key in the ignition at any time. It will ruin your ammeter!
  [3] Wait 10 min after the doors have been closed/locked. After 10 min, you should have a reading below 50mA.
  [4] If above 50mA or so, take out the fuse for the interior lighting, close doors, wait 10 min and measure again.
  [5] Sit in the car for 10 min and listen after buzz-sounds, relays etc. Anything unusual and it means current drain.
  [6] Still too high, take a picture of the fuse box in a good enough resolution to see all fuses. Take out all fuses,close doors, wait 10 min and measure again.
  [7] Same thing for the fuse box in the engine compartment.
  [8] When you have narrowed things to either things to either interior fuses or engine bay fuses, you need the picture you took again. Start with putting half of the fuses in the box again. Take out half of the ones you put in if things are draining battery again - if not put in half of what you have left, and so on.
  [9] Still no luck? Your ammeter might be broken
  

Hope this helps someone - battery drain is really frustrating and can be hard to find.

[eccleshill]

Great post!

[KBPhoto]

I'll bookmark this just in case. Thanks.

[Wardy]

Good work. Nice that you found the cause and solved the issue

[saksager]

Thanks guys - I just hope this will help someone, since I found a lot of diverging info on the Internet

[gregoir]

Spent a lot of time on my recent camping holiday living out of the car- so the doors and boot were open frequently. The courtesy lights timed out eventually. But after a few days the radio panel started to give a message about low battery voltage causing the radio to turn off. The car did start next time but I reckon it struggled to crank a bit. So it appears that only certain ancillaries are disconnected when the battery voltage drops......

[meta55]

the control box for the locking must be on a constant positive, as you said you pulled out the fuses with no change to amps, so does that mean there is no fuse for the box. not good if there is no safe guard.

[saksager]

the control box for the locking must be on a constant positive, as you said you pulled out the fuses with no change to amps, so does that mean there is no fuse for the box. not good if there is no safe guard.

I might have done this too early according to the hibernation time at first (and the mixed it up with some other current draw) - when I took out the power connector for the box, the amps settled instantly. Perhaps the fuse is in the engine compartment? Did not pay too much attention to which circuit the fuses were for - just wanted to find the error and the check which circuit it was for

[charles]

I've had a flat battery 3 times in the last 12 months in my 2010 FL vRS! which I found to be caused by the Bluetooth system!

The problem being that the Bluetooth is powered all the time, thus draining the battery!

My dealer has said they will re-wire it to the ignition so it's only 'on' with the ignition.

[Wardy]

Sounds like they haven't coded and/or fitted the BT kit properly then - as that shouldn't happen.

If the coding is not done properly, then it's possible that the CANBUS gateway is kept open between modules, thus causing the battery to drain as components will remain active.