98 V70 Battery Discharging

What do you mean by "full conductivity"? Zero ohms? If so, with the battery connected, a very high (theoretically infinite) current would flow - which is very unlikely!

What are the original symptoms which you are trying to investigate? Is the battery going flat with everything (apparently) turned off? If so, how long is it taking to go flat?

When re-charging a battery off the car, most chargers will drop to a trickle when the battery is nearly fully charged, so over-charging shouldn't be a problem. If the battery is completely flat, it will take quite a few hours - probably over-night - to charge fully.

You're not doing it right, you can't just measure the impedance across the leads, any capacitors in electronic devices will appear as a short circuit until they charge. You need to disconnect one battery lead, then set the meter to measure DC Amps and put one probe on the empty battery terminal and the other on the lead that normally occupies it.

But don't try to start the engine with the ammeter in series with the battery lead - unless it's a very hefty one which can handle several hundred amps - in which case it won't be much use for measuring a small leakage current.

I'm not sure how much/little current you're looking for - it depends on how quickly the battery is discharging. For example, (assuming battery capacity is linear - which it isn't, so this is only approximate) if (say) 100mA is flowing (equivalent to a 1.2 watt lamp being on) a 100 amp-hour battery would take 1000 hours (over 40 days) to discharge - so you wouldn't notice it because it would get charged up by running the engine in the meantime. So you must be looking for a lot more than this - maybe one amp or more (discharging in about 4 days). If it still happens with all the fuses out, it suggests that it must be something like leaking diodes or smoothing capacitor in the alternator. To check this, you'd have to disconnect the red cable from the alternator - but don't let the bare end of the cable touch anything earthy - so disconnect it with the battery disconnected, and insulate it before re-connecting the battery!

My V70 (UK) has also fuses in the trunk and at the end of the dash.

Dave

Can you be more specific as to where in the trunk and end of dash? Is yours a 1998?

Yes, my battery was going flat after sitting for 2 or 3 days. I tried a (newer) battery and same problem. While driving, my ScanGauge shows between 13.5 and13.7 V, so it seems the alternator is charging ok, unless those readings are low. Lights and accessories seem to work fine while driving.

I did not try to get an exact measurement on the meter: the needle went right to the peg stop. I suppose I should zero it first and get something more specific.

Thanks for your interest.

OK, I can try that. What should the reading be with this process, 0 DC amps?

Thanks!

I did consider that the amp might be the source of the leak but did not know how to test. If I can find the end of the red cable I will do as you suggest. Is it accessible from the engine compartment or must I crawl in the dirty snow under the car? (Located in Toronto.)

Yes.

You should see no more than a few tens of milliamps.

Mine is a 2004. Looking from the rear of the car,there is a panel in the lefthand side just inside the tailgate. The dash box is under a cover at the right hand end of the dash.

Dave

'Fraid you can't deduce much from that - other than if it 'happens' to be in the same place. A 2004 V70 (built on the S80 platform) is a completely different animal from the 1998 model (derived from the 850).

Not sure what you mean by 'amp' but I assume that you're referring to the alternator.

This is located at the front of the engine (on the left when standing in front of the car looking into the engine compartment) under the power steering reservoir. You should be able to get at from under the bonnet/hood (depending on whether Canadians use British or American terminology!) although things like power steering reservoir and auxilliary drive belt might get in the way a bit. [I don't think it would be any easier from

Thanks Roger. I will try to find that cable and pull it to see if that makes a difference.

We call it the "hood" not "bonnet" by the way!

Shame on you!

We do spell it neighbour (and colour etc.) But we wear our boots on our feet and Wellingtons are for flying.

OK, I zeroed my meter and redid the tests:

Resistance seems to be around 10 ohms, if I am reading it correctly, with battery removed.

I also did the test with the battery in and there seems to be 3 amps coming through.

I also did both tests with the red/white wire removed from the alternator and no difference.

Thoughts?

Ignore the resistance, as I said before, that's a worthless measurement in this case.

If you mean the thin red and white wire - that's only the sensor for the instrument lamp - you need to disconnect the *thick* red wire!

Agreed. But I've never seen a 36watt lamp in a glovebox!