Pretty new to the XJR and know after reading the forums AND having an S Type R before the XJ. That these cars don't like sitting without use!

I had family problem and had to leave the XJ at the airport for a little over 6 weeks and was sure the car would be dead when I got back.

But no problem at all and she started right up with no errors and I still have both factory batteries! Drove about 50 miles home and did notice the ECO mode did not seem to kick in. So maybe the small battery is still charging up?

I thought I read that after many customer complaints the later XJ's had an improved BMS (Battery Monitory System)?

The only info I have is dated 2011. See attached PDF.
.
.
.

 

I own a 2015 XF 3.0 SC AWD and also had problems with Eco Mode not working. Car still under warranty so I brought it to dealer. Both me and my service advisor agreed that it is the smaller battery that could be the problem.

My service advisor was absolutely sure that the smaller battery controlled the operation of Eco Mode.

After waiting for about an hour the service advisor approached me and said that it was my larger battery and not the smaller battery that was the cause of the problem.

They replaced the larger battery with an InterState AGM 950 CCA battery and have not had this problem since then. This was several months ago.

I am not very knowledgeable about automotive electronics but you would expect the service advisor to know what does what in the car and this guy was so insistent that the larger battery had nothing to do with the Eco Start/
Stop function. So make sure that the larger battery is also tested because it in some way can affect the operation of the Start/Stop function.

 

The small battery is there to keep the systems running when the ECO mode is operational and the large battery is used to run the starter. So it can be either battery that causes the issue.

 

My 2014 XJL ECO mode rarely kicks in. And I frequently get the low-battery alert. I charge the battery with a charger once every 2 months or so and then it works better. The Jaguar charging system has some design flaws in it. I would not worry too much about ECO it most likely does more damage than any "ECO" help it provides.

 

I was surprised the car started after sitting 6 weeks! People have posted starting problems after sitting only a few days and hoped the BMS had been improved in the later XJ's?

Now the ECO function is working fine after a bit more driving.
.
.
.

 

I think if it's locked up they lost a lot longer. I sometimes forget to lock it in my garage and it dies in about 2 weeks. If it's locked it seems to last quite a while longer. I've gone well over a month locked and it starts right up.

 

That applies to all recent Jaguars.

The worst thing to do is leave them unlocked in the garage with the key in the ignition followed by key out but not locked or the alarm set.

The recommended procedure is to lock and set the alarm. This allows the modules to go into 'sleep' mode with minimum power consumption.

In addition, for vehicles with keyless entry, the Smartkey should be a minimum 5 metres away from the vehicle.

Another battery drain I discovered the hard way is leaving an OBD II Bluetooth adapter for TorquePro in the diagnostics port. The port is permanently live and this flattens the battery remarkably quickly.

Graham