Confusing flat battery

[graeme]

Advice please.

I've got a completely and utterly dead battery almost overnight... It's emptier than Shug in a knocking-shop!

I can't think of anything that's live and would drain it so fast. The radio faceplate lives in the house, there was nothing plugged into the fag-lighter, and all the lights were turned off (including the interior one).

Bad earth? Where are all the earth points so I can check?
Faulty brake-light switch? How is this checked/adjusted?
Any more suggestions please?

Also, as the battery is now completely dead, can I jump start it, or will the battery be goosed and need replaced?

TIA.

Cheers,
Graeme

[robin]

Lead acid batteries survive a few deep discharges, so if it was an electrical fault that drained it, you'll be OK. Of course the battery could just be gubbed anyway.

First order of the day, jump start it.

Disconnect jump leads and measure voltage using a multimeter - you should see > 14v implying the alternator is charging the battery. If not, that's your problem.

If it is charging, go for a run to put some charge in the battery (try not to stall!).

Now switch off engine and turn on the full beam headlights.

Using multimeter, measure battery voltage. It should still be >12v. If it's <12V the battery is gubbed.

Now, get someone to crank the starter while you measure the battery voltage. If it drops <8v while cranking, the battery is gubbed (and the start probably won't crank either).

If the battery & alternator appear OK, you have to work out where the current is going.

Once you have got a recharged battery, disarm the alarm, disconnect the -ve terminal of the battery.

Set your multi-meter to the 10A current measurement (and you'll probably need to replug the red lead on the multimeter into the 10A measurement connector instead of the normal place), then connect the black lead to the -ve battery lead and the red lead to the -ve battery terminal. Take a look at the current indicated - it should be <0.1A - if it's more you need to go work out where that current is flowing - we'll worry about that later!

Cheers,
Robin

[MacK]

... It's emptier than Shug in a knocking-shop!

/Coffee ~> computer screen,,,,,, wipe screen/

[Shug]

*
































*

[graeme]

Thanks for the advice Robin. That's my evening taken care of.

Graeme

PS Sorry Shug. First beer on me next weekend

[Shug]

...Deffo do the Robin route of tracing it properly (as I usually don't) But I'll lay a fiver on it being the brake light switch in the end....

[mattg]

Hi guys,

Did anyone manage to find the cause of this problem?
I have this problem with my '00 S1 111S.
It happened last week for the first time, cant think of anything I did with the car, but immedietly thought it was the battery and went out and bought a new one which i fitted on Friday night. Car was fine.

I did a 50mile run on saturday, then a 100+mile run on sunday, car went a-ok.
On Monday morning - same as last week - nothing, not even a flashing 'alarm' indicator, radio faceplate was removed. I did activate my alarm, but then i normally do that anyway.

Thanks,
Matt

[graeme]

Well, it charged fine and has been 100% reliable ever since. However, I have just recalled that we had to adjust my brakelight switch in the carpark at Ft Bill on TT07, so it was probably that.

[mattg]

thanks graeme, where is the brakelight switch located and what sort of adjustment did you have to make to it?

rgds,
Matthew

[graeme]

It's in the front service compartment, reachable with a small hand. It's above the pedal box under the top of the front clam and under the windscreen, in. You'll feel the wee screw thing on the end. You'll probably need to park backed up to a wall to see when the lights are on, and have a helper to press the pedal while you adjust.

I don't have any pics of its location, and the service manual doesn't seem to mention it...