Hi all. This is my virginal post, I’m at my wits end. It may me a while to get trough this, a few days back the alarm went off on my XJ 351 whilst parked in the car park at work got the key & reset the alarm all good here I thought, later in the day walked back to the car in the poring rain put my bag in the boot still all good, opened the drivers door & the sun opened on tilt still persisting it down with rain I thought this ain’t good so proceeded try to shut said roof to no avail, after a few seconds message on dash said start engine battery low, ok did that with no issue at all, next thing you know the sunroof decides to open fully not good as it’s still chucking it down, it appeared that once the battery had received some charge it closed with no effort. Got home parked the car pressed the stop button the what do you know the sunroof pops open again tried to close it it’s having none of it every time I shut the engine down the roof pops up, the only way I could get it to stay closed was to hold my finger on the close button whilst stopping the engine. So after asking around I came to the conclusion that because I hadn’t been using the car only to do the six each way to work & back i was taking more out of the battery than putting in, so decided to put the battery on charge before the charge my meter read 12.1 after the charge I checked it again & it fine at 12.5, since then it had been fine until this morning at around 4am the alarm is freaking out again, every time I do the reset two mins later off it goes again so on checking the voltage again it’s down to 12.2 put it back on charge still not able to shut the dam thing up so decided to go for drive up & down the local M/way came back it’s now back up to 12.5 great I thought at least the charging is working. I shut the bonnet & proceeded to try to lock the car what do you know I now can’t lock it with the button on the remote or the buttons on any of the door handles but the remote will open the car or at least go through the motions ie flashing indicators.
Whilst out for the drive there was one thing I noticed & that was as I got onto the motorway it was like the electrics had a little cough the lights went off the dash went off only for a nano second then it was back to normal I was still accelerating at around 65mph with no power loss it purred along at 70mph for over an hour with no other probs.
please does anyone have any clues as to what is going on with it,
the car is five years old now with only 29k on the clock.
(is it the battery I don’t know )

 

You need a new AGM primary battery, no doubt about it. All sorts of electrical gremlins happen when the battery is low, and your XJ gave you a warning. You may also need a secondary Stop-Start battery, but I'm not sure if your XJ has the same system as in my 2013.

With only 29K miles in 5 years, it appears that you don't drive far enough every day for the alternator to bring the battery up to a full charge. If that's the case, I recommend that you get a battery maintainer that will keep the battery topped up automatically. I know that you have a battery charger, but that's a different animal. I have a CTEK brand maintainer and recommend it.

See:
https://www.jaguarforums.com/forum/x...lation-130801/
https://www.jaguarforums.com/forum/x...attery-212478/

 

My first suggestion would be to try paragraphs.

 

Alarm shouldn't go off if the battery is low should it ? My moneys on a bonnet or door sensor

 

Yes replace the battery first and report back. It's a simple fix and a very common problem.

Let us know how it works out?
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First of all thanks for all your very quick responses it’s very much appreciated.
it seems I have the same set up as your pictures show Stuart, the only difference is the colour of the spare wheel, mine is orange. (Pictures were great By the way thanks)
ive been to the jaguar dealership, they said the same as your posts but wanted £174 a minimum of an hours labour,
I decided to take the Indy route to see what they say £36 perfect, complete with Dual battery test.
the stop start battery was fine, the large battery condition was fine 100% but was only 58% charged, this was after I had done quite a lot of running around.
they suggest a full over night charge ‘ may be turn off the stop/start as well.
they did find some ghost codes which they deleted & three or four in the body control unit which try could not,
one was the rain sensor the others were auto headlights & door & bonnet sensors.
The car is booked in for a service in the next couple of days I’m going to see if they will incorporate the plug in as well.
so that’s where I am at the moment.
Im interested in the battery maintaining device a couple of you have mentioned, got my eye on a CTEK 7.0, do You think I could clip this onto the jump start lugs under the bonnet.

 

Using the remote battery terminals should work. I use them with my XKR because they're easier to access than the battery, which is in a separate compartment. See my posts ## 17, 19, and 21: https://www.jaguarforums.com/forum/x...lay-ups-73471/