[Markr]

Assuming you were trying to jump start because of a flat battery, have you resolved that, and if so what voltage do you get across the battery. Should be at least 12.6v, anything lower needs charging and less than 12.2v and not charging above that, is scrap.

After charging, you need to put a load across for a couple of mins, to take away any residual charge, so you get a true view. At Jaguar, they used to put a 55w bulb across for 2 mins.

The XJ was very temperamental around battery voltage, and dropping below 12.4v used to unleash a barrage of messages, ABS fail, ASC fail etc