Something draining my battery?

[Quatrelle]

I recently changed my 6-year-old battery, because for the previous few months it didn't seem to be holding a charge (it didn't take long for it to drop to just over 12v), and failed to start the car after it had been standing for less than a week.

Unfortunately the new one seems to be doing exactly the same thing. I've checked and cleaned all connections, and a meter put across the terminals when idling shows 14-15 volts going in. I've kept the old one, and sitting on the bench in my garage holds its charge longer than the new one on the car.

There's no alarm fitted, and no other accessories other than an aftermarket rear parking sensor fitted just after I bought the car 10 years ago. It's garaged, locked, and the weather's more than warm enough to have no effect.

Any thoughts on what could be taking the power? I don't have VCDS, and am reluctant to bother with the cheapo Chinese scanner that I use on my mate's wife's Renault.

Thanks in advance
Q

[zollaf]

use your meter on amps. remove the earth lead from the battery and re connect through the meter. close the bonnet latch so it thinks the bonnet is closed, and lock the car. after 20 minutes everything should have gone to sleep and you cans see how much electricity is going out. could be a boot light or glovebox light staying on so rule those out first as after that its something thats actually faulty. check by pulling fuses until the amps drop to almost zero.

[RichardSEL]

As per Zollaf's reply. When in sleep mode the current (measuring the battery volts won't help) i.e. with meter in series with the negative battery terminal and chassis should be max 50mA. So when you've put your meter in series, closed the bonnet, and left car for 10 mins to go into sleep mode you start out with the highest DC amps range you've got on your meter and gradually reduce the range down until you've got a reading the needle (or LCD display) gives.

Still use an olde Avominor that's only got a maximum of a 1A DC current range, but goes down in steps: 100mA, 10mA, 1mA, and .1mA

[Quatrelle]

Thanks both for the replies. I'll do some follow-up when I've bought another meter - it gave up measuring amps a while ago after I lent out.

In the meantime I'll put the Laguna battery on the Passat overnight just to eliminate definitively that it's not the battery.

[Quatrelle]

Got a new meter.

Silly question time - once I've connected the meter, shut the bonnet and locked and left the car to go into sleep mode, I'll need to unlock it again to access the fuses inside the car and under the bonnet. Won't unlocking the car wake it up?

I can dismantle my old MG with a box of spanners, but these modern 4-wheeled computers are way beyond me.

[RichardSEL]

Well, yes but let's see what current reading you get when it's locked up and asleep?

It's the jaberwockies that come in the night and steal your milliamps, one by one. They wait until you're asleep

[Quatrelle]

Deep joy - got the meter all set up, sitting on the bonnet, everything locked and waiting for the car to go to sleep. Went in for some lunch, came out an hour later and it was raining, hard (unusually, the car's sitting outside its garage for reasons I won't bore you with). Thought I'd turn the meter on anyway, no point in getting wet when you can get soaked, and it showed a row of zeroes.

Pulled the wires out of the meter and took it in to try to dry it, haven't bothered to open it, I'm just a shade pee'd off.

Anyway, I'm out of here till at least the weekend. My wife's already in the UK (serious illness on her side of the family), so a meter is the least of my worries right now.

Follow-up will eventually follow. Thanks again.

[Quatrelle]

OK, back on it. There is no abnormal drain. However, while I've been away it occurred to me that about 6 months ago I found the battery flat (usual flashing dash lights etc. 9V on the meter). I thought at the time it was where I'd used the battery to start our old Laguna (battery totally knackered, jump leads only good enough for a petrol engine), and not tightened one of the battery post clamps when I replaced it.

Alternator seems to be working ok, I've got one of those cheapo voltmeters that plug into the cigarette lighter.

I'm guessing there's an intermittent fault somewhere, so I'll go over all the obvious connections and make sure they're clean. I'll start by leaving open the ski port in the back seat - should be a give-away if the boot light occasionally stays on!