I've looked at the service manual and there's no special mention of a special procedure.

The long vertical bolt that secures the plastic tab to hold the battery in place won't budge at all. I takes an 8mm socket and is very thin. If I try and twist it any harder either bold will snap of the head will round off. It's a real screwball arrangement with a terribly undersized bolt that's way too long but it is what it is.

Is there some trick to this or is the end of this thing probably corroded?

I can't see any evidence of anything on the inside though it's impossible to see.

Has anyone else run into this problem? I don't even drive the car in the snow/ice/salt.

Thanks

 

That area is subject to corrosion from underneath even though you do not drive the vehicle in the snow and ice. Allow some PB Blaster to run down to the bottom of the long bolt, then give it a day or so to work....

 

As above. the bolt hole goes right through to under the car and it rusts!
If you do snap it off, you can drill it out re-tap the hole and purchase a new bolt and clamp.

It was XR834356 but is now C2Z6792

https://www.jaguarclassicparts.com/uk/part/XR834356

Mellow

 

Kroil to the rescue. I squirted a bunch in from the top and it does puddle around the bolt at the treads and seep in but I also dribbled some on the bottom which was crucial as yes the exposed and lengthy tip was a bit rusted and that made it easier to pull back out of the threads. There's a rubber grommet there too but it was actually rusted at the base of the flange the worst and that's past the rubber grommet and inside of the trunk.

It began raining and blowing as I went back and forth but now it's done. This one is 3 years old and the one I took out is over 6 but still charged and started the car fine.
Hopefully the spurious codes stop now. But ...

Update: It didn't but I know the battery was fading anyway 12.49 vs 12.89 now.

 

Kroil is excellent stuff. Eventually is will seep around the crimped seams on the base of the can; it is truly "the oil that creeps"....

 

On a long bolt that I'm sure will break here is what I do.
1. Using a wire brush remove as much rust around and on the threads as you can.
2. Soak for at least 24hrs in a penetrating oil (multiple applications of oil from every angle)
3. Use only a tight fitting 6 point socket
4. Using a hammer and punch or shaft tap the bolt along its axis. The point is to concentrate as much force as you can w/o hurting anything.
5. Using a vise grip grab the shaft in at least one area as close to the seized threads as you can.
6. Both tighten and loosen the bolt to get it to rotate even the smallest amount.
7. Applying equal torque on the socket and vise grip unscrew and screw the bolt working it back an forth.

Often times the rust / corrosion will build up as your unscrewing. Don't force it though that stage! Continue to use a wire brush and keep working it back an forth. (brake caliper bleeder screws anyone? ;-) )

Using this type of care I've seldom found a fastener I can't remove. And I've even removed some that professional mechanics has given up on.
With time and gentleness they will almost always come out.