V50 New battery yesterday. Flat today.
 

I jump started my battery the other day but the following morning it was flat again. I swapped it out for a brand new battery and it started fine. This morning, dead again.
So it's not the battery but something drawing current. Everything is 'off' and there's no chargers or the like plugged in.
Any ideas?

With your battery charged up, if you can lay your hands on a multimeter (a cheap one is only £10 or so), do the following:

Make sure everything in the car is switched off, doors closed etc.

Disconnect the positive lead from the battery. Select an amp range on the meter, attach one multimeter probe to the positive battery terminal, the other to the cars positive battery lead (I use a couple of large clips I have for the purpose).. You are now reading what current the car is drawing "at rest". It should be somewhere between 25 and 40 milliamps.

With what you are describing, it would suggest you have a drain of 2 or 3 amps or more going on.

Now, one at a time, pull your fuses until you find the offending circuit. Now you can start to investigate each item on that circuit.

Usual culprits are often things like door marker lamps staying on when the doors are shut, glove box lamps remaining on, boot lamps remaining on , all of which aren't visible. Interior lamps staying on is another but you should be able to see that. However, your current drain sounds like it is something heavier duty than that.

Regards
John

Hi John.
Thanks for your advice.
I've had the new battery disconnected now for a couple of days.
Before I tried working on it today, I tested the battery and it's good.

I connected the positive head to see would it start today but it's still the same. There was a clicking sound from or near the fuse box to the right of the batter and no alarm sounding.
There wasn't even any lights going on in the dash (clock etc.)
I disconnected the positive again and I purchased a multimeter.

I Checked the current as you described and it's showing that it's drawing 13Amps at rest (no key in ignition - nothing in the car 'on').
I checked every fuse under the bonnet & under glove box - all are good.
13Amps to me seems massive.
I am at a loss as to what is the culprit.

From a response I gave in a similar thread. The quickest way to get an idea of alternator performance is to measure the DC output directly from the alternator b+ post not the battery on a running engine.

Thanks!
I think you are on to something. It could be faulty diode on the alternator draining power.
I'm not testing on a running engine as it won't start. I assume you mean to jump start the car then do the test?

Yes ideally and a failed diode would show a hugely reduced alternator output <11v DC.

Alternatively, with the engine off you can disconnect the negative battery lead then the alternator live lead then use a multimeter to do a diode test both ways between the alternator b+ post and alternator casing.
On the diode test, you're looking for around 500-800 with red meter lead on casing and black meter lead on b+ and open circuit/ol/no reading with red meter lead on b+ and black meter lead on the casing.
If you get a reading both ways on the diode test, you have a failed diode.

Hi again,

You say you checked the battery and its ok yet you still cant start the car. Although it's called a 12v battery, a fully charged one should give you a reading of 12.6v! A read of 12.1 volts or less would mean that you would be unlikely to be able to start the car or even crank it over slowly as at that voltage it is about 85% discharged.

To do the fuse check you ideally need a fully charged battery whether you are pulling each fuse out n turn and seeing the effect on current drain or doing a voltage drop test. If you have pulled out each fuse in turn and none of them have made any difference, that's eliminated just about all the circuits in the car as virtually everything is fuse protected.

The advice you have been given here is good - an alternator fault is not uncommon and could cause the sort of current drain you describe - 13A is horrendous - so I would certainly start investigating the alternator.

It's hard to think of other causes for that discharge rate that wouldn't be immediately obvious. If you had wiring somewhere that was shorting out, that would blow the fuse on that circuit and the current drain would cease. At your discharge rate a 72aH battery (the heavy duty one) would go flat from fully charged in 5 to 6 hours.

Regards
John

What you say you can't start the car what's actually happening?

Are you getting anything? Have you checked the 150 amp main fuses from the battery?

Basically I'm having a similar issue with our V50. Rather than to start a new topic, it seemed appropiate to me to add to this one. If this was wrong, I apologize.

We did not place a new battery (yet). I can charge the battery today, using an external charger, and then tomorrow it is empty again.

I measured the current with the car switched completely off, keys not in ignition. It measures in at 2.5A, wich is way too high.

What I believe is happening.. our V50 is a DrivE model, so it has the start/stop system. This sytem has stopped working some time ago. I used vida to get error codes and there was an error for the start/stop battery.

As we don't use start stop, and that battery is rather expensive for what it is, I decided to leave it at that.

I think the car is using the main battery to charge the start/stop battery. And since that one is broken, it drains the main battery.

Also when the main battery is low and we start, it sometimes happen the first start is a bodged failed attempt like if the battery is dead, and then the second time it starts up normally.

My theory is that it first tries to start from the defective start/stop battery, and if that fails, then uses the main battery.

Am I correct in my assumptions?

If so, is it possible to disconnect the start/stop battery without wrenching ?

I'd remove the start stop battery if Volvo hadn't decided to put it in an impossible location. What moron puts a battery in a car so that you have to remove a bumper to reach it?!

The start-stop battery should not charge from the main battery, It should be isolated when the ignition is off by a system of diodes and relays. It only charges when the engine is running.

The start-stop battery does not actually start the car, it's only reason for existence is to provide a secondary 12v supply to ensure that the power to ECUs, lights, radio is stable and doesn't drop out when the main battery voltage dips due to the load from the starter motor (re-)starting the engine.

If you start the car while the headlights are on, and the brightness of the headlights doesn't change significantly while the starter motor is running, then your start/stop battery is OK. But you may still need to run the battery calibration in VIDA to get the start/stop function to work.