I’ve seen various posts about batteries, good/bad/checking voltage..etc. Here’s my recent issue with my ‘97 xk8(74K miles); turned on the a/c and shortly noticed the battery gauge dropped a bit. Highway driving , 70-75mph. Turned off a/c, gauge went right back to perfect. I keep a close eye on all those quirky gauges, so this was a first. No issues at all with anything else. I don’t have access to the service records right now, but I do remember that the battery has been changed( number of times tbd). Off the top of your exceedingly clever heads, any tips, suggestions, advice? I may have a new mechanic on the horizon and hope to ask him questions and/or anticipate possible problems. As usual, likely overthinking this…Thank you!!

 

When the A/C is engaged, both of the cooling fans are running at max. They draw a relatively large amount of power in this mode so it may just be that which is dropping the battery voltage a little.

If you're not having any other issues then I'd just make a note. "Keep calm and carry on", they say.

 

So right… li need to literally have that on post-its in every corner and that includes the car. Thank you for the reassurance! In another car, I had the alternator fail twice… a most unpleasant experience.

 

The voltmeter is a fake gauge ..it has 3 computer controlled positions ...in the centre ..computer thinks all is well. Hard to the left ..not charging .. Hard right overcharging.
So you is OK

 

Your battery should have a sticker somewhere on its casing showing a four-digit code. The first two digits are the month and the last two digits are the year that your battery was manufactured....

 

Those gauges are nuts. I read a bit about them when I first looked at the car. They’re either fine with some leeway….or not so fine. Jaguar designers were having a bit of a laugh at paranoid folk.
Thank you!!