I've read most of the threads here on the XK8 battery discharge issue but still fail to understand why I would have to keep my battery on a trickle charger when not in use. I have left other vehicles for 9 months to a year through winter conditions and was still able to start them come spring. What's with the XK8 electrical system that needs to have this trickle charger "Band-Aid" approach?

 

The car doesn't drain the battery. That's not the issue. Car batteries naturally loose charge over time. The problem is that allowing the car to sit without a trickle charger for months on end will be a bad time for you even if the cars starts just fine. You will see many unrelated warnings messages: suspension fault, transmission fault, restricted performance, ABS fault, traction control fault, airbag warnings, odd OBD II fault codes, the windows will not raise after closing the door, and other weird stuff. This is because the Jag's canbus system is very sensitive to voltage differences. None of these messages would light up on your dash with a fully charged battery unless there really is an issue with its associated system. Keep the battery charged and the next time you want to enjoy the Jag, it will be happy to reward you.

 

Thanks for the reply Giandanielxk8. I understand and appreciate that all batteries will "air discharge" over time if left unattended, but in one week???. I drove the car last weekend extensively, parked it for the week then went to start it again this past Saturday and the battery was so dead it registered 10.4 volts on my multi-meter. I checked to ensure I had not left on any lights or obvious accessories.

 

This doesn't seem right. I'd check your battery, then the 'quiescent draw' with a voltmenter/ammeter in the battery circuit. Next stop, alternator. It also draws more power when it's not locked, which I still forget to do almost everywhere. It's also old...

But, in general, the car has a bunch of electrical demand, especially in the summer. The 'factor of safety' given to the car electricals appears to be closer to the capacity of the alternator/battery than in many other cars.

 

I agree with Dale. There is something not right there. I've left mine without starting for about a month, usually when waiting on parts, and it always starts right up with no issues. It's currently been a week since I last drove it; I'm waiting on a radiator, and I'm certain it will startup with no issue.

 

Thanks, Dale. So you're saying that these cars will draw less battery current when locked unattended then when left unlocked? Something to do with the security system?

 

So the consensus is that there are vampire draws on my battery that I have to track down. Makes sense since it doesn't make sense that a healthy battery would deep discharge in the span of one week. I have some sleuthing to do.

 

No worries. Don't know exactly what is turned off/put into reduced power mode when it's locked, someone here probably does. More helpful information below.

https://www.jaguarforums.com/forum/x...y-drain-73957/

 

Thanks! Signing off for this evening. Great info. Thanks to all .

 

I'm sure you must have read my posts on my same problem. The final solution was to disconnect the battery for long down times. like a month or more. For a few days when it goes dead it is probably the radio not turning off or the ignition switch not turning the radio off. My solution was to pull the radio 10 amp fuse located in the fuse rack in the right door post covered when the door is closed. The 10 amp is read and at the bottom of the row most forward. You might test that to be sure you have the right one. When I want to listen to the radio I put it back in and remove it again after use. Simple.

 

Thanks for the info EZDriver. Pulling the radio fuse seems like a better idea since disconnecting the entire battery means having the ECM do a cold re-boot when the battery is reconnected. What a shame that we have to resort to these methods on such an over-engineered vehicle. Seems like they have to put the UK Engineers to work doing "something". I personally would be happy if I could disconnect about half of what this vehicle chooses to do automatically!. Thanks Again.

 

Happy to help diagnose the issue - either:

a) you have parasitic/vampire drain which is a fault in the car, could be any number of things.
b) you have a dead/dying/internally shorted battery.
c) you have a charging system issue

First test - disconnect the battery when you are next not planning to use it. Measure V after an hour then after a week. Assuming you have just driven the car for say at least 30 mins then the battery should be around 12.8v after an hour, and it should be (given normal storage temperatures) not far off 12.8v after a week.
The results of this test will tell you bad battery, charging system problem or parasitic drain. We already have a comparison as you said it was 10.4v after being connected for a week.
When we know which one of the 3 problems it is likely to be we can go to stage 2..

 

Sounds like a sensible approach. I'm travelling on business and so will first be able to accomplish this on Sat, 9/5. I will report results to this forum thereafter. Thanks for all the great input.

 

Any update on this ?

 

I had a parasitic draw on my 2000 XK8 due to the shutter in the ignition key slot sticking open. A quick shot of lock oil took care of the problem. The shutter operates a switch which turns on various functions when you insert the key.

 

Powdered graphite is also an effective lube for that ignition switch trap door....

 

Just curious what various functions are controlled by the shutter? Makes me wonder as some stuff seems to be always on.

 

No Update dispite the great advice. I just haven't had the time in the last few weeks to even drive the car (poor me!). It's sitting connected to a maintenance charger.until I can get some play time.