Golf draining battery

How did you test the battery? It sounds like it is borderline faulty to me.

is it the original battery and how was it tested?

The AA tested the battery, I was not there so I do not know what they used.

Generally they just test the starting current & volt drop is good enough, not the capacity.

The AA have a pretty sophisticated set-up for this; as long as the operator used it correctly, the diagnosis will be accurate.

If you are going to leave the car for a few days, can you disconnect the battery? If it starts fine after that, you will know you have something draining it to excess.

Prime candidates are boot or glovebox lights staying on.

Chris

I'll get it fully charged up and nip it down to the garage for a proper test.

In the good old days I would have just stuck a multimeter on a 10A setting in series with the battery.

It's not something I would want do on a newer car, I have no idea what power could be used when you connect up a battery (bloody electric everything).

If it was anything even remotely approaching 10A, it wouldn't even hold a charge overnight. Typical values might be in the 20-50mA range.

If you are worried about destroying your meter, use a fairly high wattage lamp in place of the meter initially; the lamp should barely glow.

Chris

Surely it shouldn't glow at all if things are ok?

Are there not start up currents. For example I seem to remember that my old Cavalier used to automatically wind up the windows and lock the doors when you connected a battery (not that I had left my car keys inside when I did swap the battery!)

But start up currents (see my other post).

if you connect the meter leads to the battery terminal and the battery lead BEFORE you pull the lead off then the initial higher current flow will be dealt with. The most likely fault is still the battery just by age.

All (modern) cars have some current drain; whether or not the lamp glowed would depend on the amount of drain for that vehicle, and the wattage of lamp used.

Chris

So simple, but so brilliant. Thank you.

I'll test it in the morning (it's at my parents house). And if there is a high current draw then I just need to pull the fuses out one by one to find the dodgy circuit and start from there.

Best to measure the current being drawn with everything off. You'll know how to do this. ;-)

Start with a high setting on your DVM (10 amps) initially as re-connecting the battery can take a high current for a short time. Then switch it to a lower setting. If your meter needs the leads re-plugged, short across them while doing this.

Most cars will be less than 0.040A. If several amps, disconnect the alternator output (thick wire) and check again.

I have warned my Dad that I am not prepared to bugger about wasting my time on the AAs word that the battery is OK. He has to take the battery for a proper test or buy a new battery before I start any tests.

And proper test means a fully charged battery tested at the local motor factors with a proper tester not a cig lighter plug in device.

I've just noticed that it's a 7 years old Golf; does it have a perimeter alarm/keyless entry?

If so, even when new and with a fully charged battery, they will go flat in two weeks.

There were many disgruntled owners returning from holiday beating a path to the dealers, only to be told "They all do that Sir"!

Chris

interesting fault possibility is the accessory relay. It should remain active for a short time after ign off so that the windows can be closed, but if it arcs its contacts together it can remain 'powered' and drawing current. So it will show up as excess current draw with everything off. A google shows that many people have a similar problem to the OP, with many possible solutions.

So as ever, best to measure accurately the quiescent battery load - ie what things like the immobiliser etc take when nothing is apparently switched on. Wish there was a reliable clamp meter for measuring these small currents at a sensible price, to avoid having to disconnect the battery.