I bought a Ronsol multimeter and did a test on the battery to see if tells me anything as the car starts first crank easily, it's just the electrics and weird stuff happening intermittently..

Screen freezes on jaguar loading sometimes, mirror controls non functioning, abs light, engine light, DSC light, "cruise not available", "restricted performance", limp mode sometimes, literally like a Christmas tree.

It's like the car has a mind of it's own.. all these lights came on one day, an they were on for the day... next day nothing.. not even engine light.. but following day might just be the engine light..

Also the adaptive headlight issue is on but I'm almost certain that's down to the AFS module in the footwell under the dash and only one headlight is working, but when ballast is swapped over it switches.

with engine off I put multimeter to the terminals and they read:

Engine off: 12.2
Idle: 14.7

I forgot what it went to when i put heating on and radio but it seemed to fluctuate a bit.

ALSO.. noticed there is a tracker installed in the car from previous owner.. it's fused near battery, and I followed the wires to behind the front of the dash where I found yet another fuse, but also a tracker there.. which was flashing.. Could this cause issues? I wouldn't really have thought so?

 

With the ignition in the OFF position for at least 30 minutes, there should be a minimum of 12.6 volts showing as available current. If your voltmeter indicates less than 12.6 volts, charge the battery for 3 to 5 hours at 2 to 5 amps, then retest. If the voltmeter still shows less than 12.6 volts, the battery is suspect and must be replaced prior to any further diagnostic work.

Many random DTCs and instrument cluster warnings are the result of a failing or weak battery.

 

Check the available voltage across the battery terminals, not via the OBD port.

 

The telltale sign of a failing battery in what you described is the Frozen Jaguar screen (or even a delayed switch to the main screen).
When I bought my car about 5 years ago it had a fairly new battery but I had the same issue and a few other quirks but the car would start right up.
I installed a new battery because of what I've read here about the screen. Have had no issues since and the screen comes right up. I do connect to the C-tek whenever the car is home and not being driven.

 

Good advice, but I'd increase both the charging amperage and charge time to at least double this.
I charge my low batteries at ten amps, and sometimes it takes eight hours or more until it's 'full'. Course, that's with variable charge rates which START at 10 and gradually decrease during charge.

 

I did leave my cheapo charger plugged in for about 2 days... I think it's a cheap version of a CTEK so technically the battery should be full? It charges fine but don't know if it's bad that it isn't staying stable? I don't know much about this.

 

A maintainer does not function the same way as a battery charger.

Use a voltmeter to read the available voltage across the battery terminals. If you aren't able to perform diagnostic tests, have a recovery van take the vehicle to a Jaguar main dealer or a competent Jaguar specialist.

Guessing on a Jaguar can become very expensive very fast.

 

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Very good. A battery reading 12.2 v indicates that the battery is at less than 50% capacity. That is not enough to power up the necessary modules in the car.

Secondly, when performing a reading when the engine is running, you are reading the generator output. Not the battery.
Fine for inquiring if the generator is operational. But it has nothing to do with the battery.

To paraphrase a one of my esteemed colleagues: "it's always the battery".

 

ahh I learnt something there. So basically, test it with nothing on and see what I get. It hasn't been started today - is it worth going out and testing it now?

 

if she's sat for +6 hours, yes.
Ireland... next the time I'm over a pint would be fine. ;-)

 

So just went out and tested it. Unlocked car, opened trunk, put mutlimeter on. Didn't start the car today at all.

11.73 / 11.74 is what came up on multimeter

 

So you have just proved that the faulty component is the battery - if it has been on the maintainer and has not taken the charge then the battery is no longer viable.
You will need a new battery but charge it fully! And when you mentioned a “cheapo version of a CTEK” you meant s cheap version of another brand, correct? Because any CTEK will fully charge a viable battery if left connected long enough - I have done that.

 

So that test was with the car sat for a day without being plugged in to a charger/maintainer.

The offbrand cheapo charger/maintainer I have is this:




Should I go plug it in for 6 hours and then retest straight away and then wait another 6 hours with it unplugged and do another test?

 

Good morning @MartinXKR .
As ​​​@sov211 suggests, the current battery is done. Finished. Kaput. On route to the great battery in the sky.
Stop wasting your time and get a new proper, correctly sized battery for the vehicle. Ensure it is fully charged before installation.
Then go for a fun drive.

 

Just took it off the maintainer after being plugged in for 6 hours - tested voltage and reads 12.12 / 12.13v after disconnecting the maintainer.

 

Replace the battery to resolve most of the issues.

 

Just think of your battery as being like this parrot: