www.jec.org.uk

Hi there,
I’m at my wits end with this one!
No power anywhere, apart from the clock!!
Hadn’t used her for a couple of weeks, then fitted a dashcam by piggy backing a fuse in the LH rear passenger fuse box. When I did that, all perfect and she ran well about 7 miles. Restarted and just before firing up, had “trac not available “ and Amber engine warning stayed on...but perfectly fine all way home.
I guessed I’d run the battery down as prior to that, I’d only used once in a month for a mile journey.
She sits outside under a cover. So I charged this morning. However, I realised, I should have disconnected negative prior to connecting the charger, came out a couple of hours later and took negative off and reconnect charger.
Charger says it’s fully charged... so off it comes. Reconnected. Nothing. Not even key fob.
Checked dashcam fuse. All ok. Took it off altogether. Checked fuses in engine bay. Found one blown (10A for no.3 I think) so yay! thought I’d cracked it. Replaced 10A fuse.
But oh no... everything exactly the same.
I’ve got a dead jaguar with no power anywhere!
I’m not electrical, so I’m not sure what to do now.
Any ideas much appreciated !!
Cheers
Stu

Stu,

First thing is to establish the true voltage of your battery. You need to use a multi-meter set to "volts, DC" on the battery terminals. 12.0v or less points to a fully discharged battery. 12.4v equates to a half discharged battery and 12.8v or slightly above indicates a battery that has sufficient voltage for general use. (That said, that test alone does not guarantee the battery has any appreciable storeage capacity) Such an issue can be investigated once you establish what voltage is at the battery terminals.

Do that test then come back to us. We can then continue the diagnostic process.

Mike K

Thanks a lot Mike!
I should have a proper multimeter but mine broke and I never got a new one.. I just relied on the little green light in the battery to tell me it was charged.
However I must admit I didn’t appreciate those very small parameters.
In the meantime I’m charging her overnight ( brand new charger, states 6 hrs from flat) so I’ll see if any change in the morning... in the meantime I’ll order a basic multimeter !
Will update.. cheers have a good evening!

Hi Mike, all - update
Charged overnight, and basically now everything works, but I didn’t start her up in the severe frost as I guess it has cured the issue. Even though a charger (and battery) says “fully charged) it was well worth it to heed your advice on the very tight parameters.
I hope anyone else reading this is taking note!

Cheers, all the best!
Stuart

A few days later, and completely dead..measured voltage, it was 2.18...I’d turned everything off and locked her up before, so that’s weird.
I put new charger on, but it did not charge until I learnt that some chargers don’t bother with anything below a certain threshold, which surely is pointless having if your battery is flat? Anyway I jumped the charger to life using jump leads from my wife’s mini then took hers off. I’m leaving it charging for 24 hours now, but it’s a mystery why it just went so flat.
I’ll check voltage tomorrow...
Do you think I may have worn it out so badly I damaged it?
Cheers

Checked after 24hrs..13.08v
Hooked it up again, but of course horn alarm sounded a couple of times until disarmed with fob.
Checked straight after .. 12.65v
Is that good? How come it went down in about 2 minutes!
Cheers

700SN,

You really need to establish if you've got a defective battery that just can't hold charge or if you've got a parasitic drain happening on the car.

As a suggestion:

Disconnect the battery. Take a voltage reading. Charge the battery on a slow charge overnight. Take a voltage reading the next morning whilst the charger is still connected. Turn off and disconnect the charger. Immediately take a battery voltage reading. Leave it 24 hrs. Take another voltage reading. If battery still reading 12.5v+, connect battery to car. Take voltage reading. Leave car unlocked (if safe to do so). Leave 24 hrs. Take voltage reading again.

Tell us what you've got!

Paul

Hi 700SN, do you have any idea of the age of your battery? From the description you wrote at the outset, I would surmise that the battery was dying, or at least on its last legs and nothing you report has yet changed that perception. Dead batteries tend to happen in our cars where the battery is over 5 years old. As others have mentioned above, you need to know if it is the battery that is defective, or you have a parasitic drain. Given that the symptoms occurred immediately after adding an electrical accessory, if the battery is not defective, then the circuit you accessed for the camera would be my next investigation point. Hope you see some 'light' soon.
Jim

Hi Gents, thanks for those suggestions!
There’s no drain from the dashcam as I disconnected it. It’s never had any other issues until now.
I just measured again after it sat there all day unlocked. Only 12.08v now...
I never knew how old the battery was, and if it was weak maybe I pushed it too far the other day. I’ll have to check the charge in the morning.. if it’s ridiculously lower suppose it looks like a new one is on the cards..

700SN,

It may well be the battery but don't condemn it just yet. Go through the process of seeing if it can hold charge as I suggested whilst not connected to the car.

A parasitic drain would ideally be measured with the ammeter on your multimeter positioned in series to the battery terminal. There are a myriad of items on the Jag that can cause this from defective boot lights, radio aerial circuits, locking systems, reverse current through a failing alternator pack etc etc.

Even a fairly simple check of checking a fully charged battery by starting the car, turning it off (only do this if the car is fully warmed beforehand AND the battery is definitely fully charged) and then checking the voltage immediately after a start and shut down can help to pinpoint the problem. Ideally doing a proper drop test on a fully charged battery is better, but you'd probably need to pop into Halfords or somewhere and ask them to do this for you.

Good luck

Paul

Thanks Paul,
Checked 24hrs later, 3.08v. I’ll charge her up again tomorrow and then measure and leave unconnected for another 24hrs just to see if she loses any charge.
Cheers
Stu

3.08v!? That is one dead battery!

To be reliable and have any chance of recharging, 11.5v is the lowest terminal voltage likely to achieve success. Anything less than 11.5v and I wouldn`t waste my time attempting a recharge. The battery is likely to constantly fail.

Mike

Ok... after leaving battery fully charged (13v) yesterday and disconnected - today it’s 12.85v!
This never happened before, as when I connected before after a full charge you could actually see the voltage drop bit every minute.
So at least it looks like I don’t need a new battery?

I’m not electrical so I am sorry to say I nit quite sure how to check a parasitic drain, I have a multimeter, not sure how to put in in series to check as Paul mentioned.
There’s no dash cam connected to the fuse box at all, it’s earthed to the body but not the positive it’s just hanging there in mid air.
The only thing I did was originally forgot to disconnect before connecting the charger. I even think I pressed the fob by mistake whilst it was charging.
Do you think I should reconnect her and start up? Would that sort of re-set everything?
Cheers
Stu

Stu,

That's interesting! It doesn't necessarily mean that your battery is ok, but it MIGHT!

I'm not sure of your level of electrical appreciation so please forgive me if this sounds patronising! It's not intended to, but I remember my late Dad, bless him, trying to teach me about electricity, its application in cars and diagnosis when I was 17. I still found it useful when explaining to my daughter as she reached driving age! So I hope it may help to understand what's going on with your car.

My Dad told me to think of electricity as water (but no to try and mix the two!). So If you think of the battery as being full of water, a voltmeter can measure the volts, or "Volume", by putting the probes between the positive and negative terminals. Hence your 12.8v. (It was probably never "really" 13v, it's just that immediately after disconnecting from a charge, it will read slightly higher.)

So we have a volume of "water". It then flows along the wires (as if they were pipes) and feeds each of the appliances. For most of the "pipes" on the car, the taps are turned off until the ignition switch turns them on. However, some of the pipes can still take a flow without the ignition such as the alarm system, courtesy lights etc. Also, the way that the pipes and taps are connected means that if there is a fault, some pipes can still have a flow or leakage even though the ignition switch "tap" is theoretically turned off. This can apply to things like the radio aerial, the alternator rectifier etc.

So, if we split our main pipe to the battery, and put our multimeter in between the two parts, we can measure the flow along the pipe and therefore how much is being pulled / escaping from the battery. We set the multimeter to "Amps" (or as my Dad explained "Along" ) and put the two probes between the two broken parts of the pipe. The meter then reads how much is flowing / escaping along that pipe. The easiest way to do that is to disconnect the negative terminal and then put one probe of the meter to the battery terminal and the other to the negative lead that you have disconnected. Of course you need to ensure that your extra bit of pipe (the multimeter) is strong enough to handle the flow that will go along it. Most cheap multimeters can handle less than 10amps whereas better models can handle higher loads. If your meter can not handle higher than 10amps, do NOT try and start or run the car with the meter connected in series in Amps mode. However, if it does have an Amps setting, it may well be able to handle small current flow with the engine off, such as you seem to be experiencing.

As an example, your battery is probably something like 100ah, which means in simple terms it can deliver 1amp of current flow for 100 hours with those 12v of volume. Some people find it easier to relate it to lights. Light bulbs are rated in terms of Watts, which is a measure of power. (Or as my Dad crudely explained Watts = "Wow"!) As an equation Amps x Volts = Watts. So a 12v 100ah battery could broadly power 100 watts (2 x headlight bulbs) for 20 hours.

So the implication of what you have said that your battery, when connected will drop from 12.8v to 3v overnight is the equivalent of leaving your headlights on. That's a big current draw as you can imagine.

There are other factors to consider once you get your head around the basics. My Dad then explained that the battery was not just the equivalent of being filled with water, it was like having fizzy water! And if all the bubbles disappeared, then the battery was flat, even though it was still physically full of liquid! Therefore, your battery voltage may be dropping not just because current is being drawn but because the battery is not able to "hold the fizz"!

One fairly crude way that you can test the "strength of the "fizz" in the battery is to start with it charged up at +12.8v, then crank the engine but prevent the car starting. On the x308, there is an inertia switch on the internal passenger A-post that could be used to cut out the fuel pump, or else pull the fuel pump fuse to stop the car starting. If you then crank the car for 15 seconds, whilst measuring the voltage across the battery terminals, the voltage should remain at 9.5v or above whilst cranking. If it doesn't you've probably got a failing battery. Another way is just to take a fully-charged battery into a garage or Halfords and ask them to do a drop test, which is a more accurate version of teh above routine.

However, if the battery does pass that test but is rapidly going flat overnight, it does seem as if you've got a large current drain happening. Putting your multimeter into Amps mode and measuring the current flow / drain as described above, should confirm that. You must remember that when these cars are first turned off and locked, they continue drawing current for 30 seconds or so until the circuits have closed down. So it can be a little difficult to clearly monitor this especially with the boot open, boot light on etc.

However, if you can monitor the flow / draw of current with the vehicle fully closed down and the draw is excessively high (even 0.5A is too high) how do you work out where is the fault? Well, you could start with the obvious ones, such as interior lights, radio aerial, immobiliser / alarm circuits (difficult) and see what happens. I know people who have pulled out every single fuse and relay on the car then put them back one at a time until they find the circuit causing the problem! I also know people who have pulled every fuse and STILL found a current draw happening!

So, some ideas perhaps as to where to start. As I said, Stu, I do apologise if I'm teaching you to suck eggs and you know all of the above!

Good luck!

Paul

Sincere thanks Paul, yeah I’m sure my late dad would know in an instant, I never got my head completely round electrics TBPH.. I will try the suggestions below, slowly ! Thanks for taking all that trouble to explain , it really helps understand at least some of it, give the confidence to start anyway!
Cheers
Stu