Well, I got my X Type back from the auto electricians today after having a new alternator and negative battery cable fitted. They put in a second alternator as a warranty job thinking the alternator was causing my battery light to come on at high revs. I am firmly convinced the real culprit was the negative battery cable as this was the piece whose fitment made the battery light problem go away.
As background, a couple of years ago I had my battery light come on and I tested the battery cables and the positive was running hot. As a result, I changed out the positive battery cable and the issue went away - note - at that time I didn't change out the negative cable as it was not running hot.
What I think happened is the resistance of the negative cable slowly increased over time causing the battery light to come on again recently. The auto electricians (wrongly I think) diagnosed the cause as the alternator and changed it out - but the issue persisted. It only went away today after the negative battery cable was replaced, with the end result being a complete swap out of battery cables, albeit with a 2 year hiatus between the positive and then negative being swapped out.
So take heed X-type owners - If you get battery light illumination, make sure you eliminate battery cable corrosion as the culprit before moving to the alternator - it could save you much money and grief!

 

In very hot weather and heavy trafffic, I would always expect to see my alternator light come on. Sydney summer plus traffic..have seen external 51 degrees/123 F reported on the LCD panel.

The positive battery lead was hot, especially near the battery end. There was corrosion. I've fitted an additional cable from the second battery terminal mount to the alternator. Replacing the existing cable was a bit fiddly due to the Jag connector....not sourced a replacement yet.

Never ever seen the issue since adding the second strap.

X-type V6 2.5L (2002) 190k km

 

Hey guys, this is a follow up of battery-light-blinks-while-driving.1699886/#post-14445981 The battery light was blinking while driving. The alternator connector was changed as it showed it had some bad contact, but the problem still persisted. I took the car again to the autoshop and the alternator voltage was very high (~17v) but only at some time intervals and the battery showed to be in good condition. So, the alternator was replaced by a new one. But guess what? The battery light stills turns on. Do you guys have any recommendation?

 

Well, yes…if you read the thread carefully you will see that the cause of the battery light illumination was a corroded cable - it can be either the negative or positive cable, or both. I had the same experience and the cause was corrosion in the negative cable.
You test by turning on lights, AC, engine running, allow it to warm up, hold your hand OVER (not ON) the cable ends at the battery. If one is significantly hotter, that is the culprit. Even better is to use a temperature gun to test the temps at the cable ends.

 

That's exactly what happened to me - they changed the alternator but the battery light persisted - it worked out that it was corroded battery cables. I would change out both your positive and negative battery cables and I am confident your problem will be solved.