1) Why do we need such a big battery? I just weighed mine and it is 59 lbs!
2) Which charger/tender do you use? I've been using an Optima digital 400, just because I have Optima batteries in my other cars.

 

Yeah, it is a bit larger and heavier than any other vehicle I've owned.
It's also the only one I've ever had that lasted over 10 years. It's always started the car and I only replaced it when the window dip function acted up.
I guess what I'm saying is that bigger may be better.
I have a couple of chargers. One is a trickle charger from Harbor Freight and the other is a 6/1.5/.035 amp charger from Sears that I've had for decades.
I don't think the battery cares what I use as long as the charger functions properly. It's more about what I need from the charger.
I just installed an electrical service panel in the trunk and put a 12 volt plug on the end of the Harbor Freight trickle charger, which is maintaining the battery right now.
It's a sweet set up.

 

CTEK (56-353) MULTI US 7002.

And if a larger battery would fit, I'd consider installing it. The battery capacity vs various circumstances that might drain it appears to be closer to 'the line' than I have previously been used to.

Second alternator and engine to run it too...

 

Make sure you keep watch on that HF unit. I've had three rather scary incidents involving "budget priced" battery maintainers. The problem is when they fail, they don't fail "off" but rather they fail in the "full on" mode, i.e. they don't stop charging when the battery is fully charged or there's a current drain they can't keep up with or short circuit or other charging problem. After a battery explosion that scared the crap out of me (batteries make a small amount of hydrogen gas when they overcharge), I threw all my budget units in the trash bin, got online and ordered four of the CTEK units because they have "smart" circuitry that detects charging problems and shuts the unit down. The older Diehard unit you've got is probably reasonably reliable (they don't make'm like that anymore). I had one from back in the day that still worked fine, but still I stopped using it just because it didn't have any of that "smart" circuitry. I figure my cars are relatively expensive, not to mention the building they're in. If you're going to be out in the garage every day where you can see, hear and smell but if you're going to leave it unattended for a time, consider investing in a unit with more safety features. I'd leave the HF unit for the cattle rancher's electric fence or gate opener battery.

 

My car was registered in January of 2007. I've not owned it from new, but the battery looks like an original and there's no record of it ever being replaced. I keep it on a CTek and it hasn't given any signs of failing. However, I occasionally consider a replacement as a precaution.

 

@Peter3442 If you have the original Jaguar battery the wk/yr is stamped into the top of the negative -ve terminal.

 

New info that might explain why the big battery. I put an ammeter in line with the battery. With the car off I read 0.5 amps, or 500 milliamps (ma). This is 10 to 20 times what a typical car would draw. Where is all that current going? I don't know...yet. But that much current will completely drain my big 95 amp-hour battery in 8 days or less.
I put a smaller battery (57 amp-hour) in the car and drove around. No problems at all. But it would only last 5 days tops when sitting.
Now maybe my car is just an oddball. But I suggest if your XK8/R is gonna sit for more than a few days you put a battery tender on it.
Mine is a 2001. Maybe Jaguar changed things in later years.

 

This seems like too much, except transiently at the beginning, especially while the lights are winding down. See this thread (posts #1 and #3 which include X100 data)

https://www.jaguarforums.com/forum/s...-drain-123535/

This is along the lines of my measurements of quiescent current draw on my 2001 and 2002 XK8's, less than 30 mA typically, except transiently during the shutdown.

 

I did the same sort of experiment once on the XJ8. Don't recall the exact numbers now, but as I recall it was just as you describe. It started out higher but then after I pushed the button to lock the car, it started dropping and within 20 seconds or so settled at a minuscule number. I kind of liken it to your laptop computer where ignition off is just in sort of sleep or standby mode, but locking the doors forces it to power down more completely. I still keep it on a CTEK though and the present AC Delco battery is eight years old.

 

Thank you, cpbass, for the link to an excellent explanation. I did as described, shut everything, locked the car and observed the current to be about 600ma. An hour later it was down to 30ma, normal for a "sleeping" car. Jaguar says the shut down sequence could take 60 minutes. What in the world could the car be doing for 60 minutes?! One could shut down a nuclear reactor faster!
I am going to repeat the test and watch to see how quickly the current drops. Will post my result.

But I still don't know why we have such a big battery.

 

I believe there is at least one emissions test that happens after shutdown, something to do with checking the integrity of the fuel tank vacuum seal. But I think it doesn't do it every time, just sometimes. There may be more.

 

Be very careful with the cheapie ($6) Harbor Freight chargers. A friend had one that melted into a plastic blob. I've used a 'wall wart' fully automatic Battery Tender for over 20 years with no problems.

 

I did a test today. When the car is buttoned up and locked there is a moment of high current, several amps, when relays and door solenoids are actuated. Then the current drops to 600ma and continues to drop until about 60 seconds, where it stabilizes at 300ma. It stays there for about 15 minutes, when it suddenly drops to 60 ma. Eventually it stabilizes at 30ma at the 1 hour point, which matches the Jag spec.
I did the test twice with two digital multimeters with the same result.
So the car is busy for an hour. I'd love to know what it is doing, but mere mortals may not be privy to that knowledge.

 

Guys, The simple solution is to just start your baby twice a week, that is if you are not driving it regularly.

 

"Just starting it twice a week" may be simple but not wise if you don't actually drive it. First, it'll take a 20 minute run to replace the juice needed just to start the car; and second, once you start the car it needs to run up to operating temperature to ensure that the oil is fully circulating. Idling it in the garage for a few minutes does more harm than good.