I need some help or suggestions on my problem. I have a 1998 XK8 convertible. It seem that the battery is draining for no reason that I know of. I believe the Alternator is going bad or is bad but my issue is when the car is sitting, the battery seems to drain almost to dead after a couple of days. I have started the car every week and haven't drove it at all. When I shut off the engine and let it sit for a few days, the battery seem to die. I charge it back up to full, start the engine and after a few minutes shut it down. The next time I go to start the car the battery is almost dead again. I repeat this process every week in order to keep the car in running shape. I know it could be a million reasons for this but was wondering if any one else had this issue. If I replace the alternator will this maybe solve the issue.... I am at a loss here.

 

I've moved your question from General Tech Help to XK8/XKR forum. This is a frequent question and members here with the same model will be able to help.

Graham

 

R, 1st thing I'd check is the flap at the ignition keyhole entrance. When you insert key, it lifts the flap closes a circuit telling car key inserted. Years of grime can jam the flap in the up or key inserted position. I've seen many folks who traced their battery drain to this!

Check it let us know. If that's not it, your feedback will prompt new suggestions.

BTW save time. If you come back to say flap is ok, not the cause. Tell us if you have a DVM and know how to use it. (That'll save a Q&A loop)

BTW alternator won't be the root cause of a slow battery drain mate.

John

 

+1 on having a multi function DVM to test for a parasitic draw if the ignition assembly isn't the cause of the battery going flat.

But, before diving in and guessing on a Jaguar, which can become very expensive very fast, use the voltmeter to read the battery voltage across the terminals with the ignition in the OFF position. If the available voltage shown on the voltmeter is less than 12.6 volts, charge the battery for five hours at 2 to 5 amps and check the voltage once again. If the voltage is still less than 12.6 volts, the battery is failing or weak and must be replaced.

If you don't drive the vehicle for extended periods, it may be wise to have a battery tender attached to the battery to keep is fully charged and lengthen its service life.

 

Another vote for using a battery tender whenever the car is not being driven overnight or longer.

Using or not using the tender may have no bearing on your issue, but it’s a simple way to keep the car free of electrical gremlins regardless of the alternator working as intended, or not.


Z

 

After 40 years as an auto electrician and consultant to jag peugeot LR and london taxi I can suggest this.
The battery is fuco. Batteries are like women unpredicatable and difficult to read . How old is it for a start but you can play a good tune on an old fiddle.
I would suggest disconnecting the negative and charge the battery for at least 12 hrs . Let it stand for another 12 hrs disconnected and measure the voltage . If its below 12,5v it may be scrap. Note the word MAY. does it have a "magic eye" Green over 50% Black below 50% Clear no electrolyte danger of explosion.
Put your ammeter between the battery Neg and the neg cable and read the current. Make sureThe doors are locked . Bring the wires out the trunk and close it or you will have the load of the trunk lights . I have read 600ma on mine but it drops as the computers shut down. Should drop to around 60 ma . If it stays high after about 30 min you got a problem.
Test the alternator.
Put your voltmeter across the battery ,start the engine and read the volts . After a few minutes should climb to at least 14v. If it does not the alternator is faulty. Some alternator faults cause a load on the battery. At night start the engine and see if the warning light is glowing dim ..if it is Diode fault.
I use a battery tender but it can disguise a fault ..ie when you dont use it for a few days the battery fails
Let me know the results for further advice.

 

I installed a battery cut off switch at the negative terminal of the battery and always switch power off when parked in the garage and won't be driving the car for a few days or more. I leave a small board across the trunk latch so when I'm ready to go some where I don't have to unlock the trunk with the key to access the switch. I just lift up the trunk and turn the switch on. This causes less use of the trunk lock and the trunk switch in the car that won't work until after power is switched on. With salt on the roads due to inclement weather all winter I probably won't have the car out more than 2-3 times until late March. This has worked for years. I think it's a sin to drive any of my old Jags on these salted roads so not much driving fun during the winter.


1998 XK8

 

What you say is fine for you but you need to reset the windows each time you use it and the gerabox has to relearn its changes. You would be advised to give it a charge in the spring as the battery has a self-discharge rate which will drag it down. The alternator will not bring it back to full charge as you need 15v for that .

 

I have been told and I'm that if I disconnect the Battery I will lose the codes for the car. 1) Is that true ? 2) the battery is brand new or was brand new but I have charged it many times now that the car has drained it (for me ) no reason. I will try the suggestions you have for me if I know that disconnecting the battery will not affect the codes. I was also told to stick a 9 volt battery thing a ma gig in the cigarette light to keep the charge in but my cigarette light doesnt work.... Let me know about the codes? and Thanks

 

Only the radio code will be lost and that should be written in the handbook. The windows are easy to re set . ( up wait for click ,down wait for click done)

How old is the battery ..4y + suspicious

 

The Battery is less than 6months

 

The flap on the ignition switch seems to be ok, it sticks a little but seems to be close. So I guess I must ne looking at something else.

 

The suggestion about the ignition switch is a good one. A little wd40 or the like should work...

You'll have to have a voltmeter, digital...

Roll DOWN the windows, leave alarm off, close the doors, unlocked wait a few for the car to start moving towards going to "sleep"...it takes a few minutes... Even better, fool the car and the "door close" switches by closing the latchs in the doors allowing the electrical system to believe the doors are closed. This is good so you can get to all the fuse boxes... Fool the hood/bonnet switches the same way. Access to under hood fuse boxes.

Open the trunk and take a screwdriver and FOOL the car into believing the trunk is closed by shoving down the clasp that flips when you close the truck to lock it. It's in that dark and mysterious hole/space at the bottom center of the trunk/boot door.

The boot lights should go out.

Disconnect the negative cable to the battery...

Take your meter and switch the positive lead to the 20amp slot. Turn the DMM to the 20amp (or more) setting. You'll need to place the POS DMM lead onto the negative post of the battery using a clamp or vise grip of some kind. Pin the NEG DMM lead into the negative battery cable/clamp somehow.

What does the volt meter read? At first, when you close the circuit with the INLINE meter connections, the amps will start UP a bit, a bit high, but you will notice them settling out pretty quickly.

​​​​​​The pain,,,, the process of removing alllllll the fuses one by one until you find the system that is causing the problem - then the fun work begins...

On mine,,, it was the NAV system. I pulled the fuse. Problem "solved"... Actually, this week, I just removed all the pile of audio stuff from the boot - thankfully the amp still worked fine these last weeks and months BUT the CD player and NAV system looked like a haunted house inside. I decided I need to just replace them. Played my first CDs today and the NAV system (which is completely outdated) is in the mail as we speak. Anyways... You've got a little digging to do,,,, which is good! You'll learn a ton about the car...

 

Mm on the 1998 disco the battery cause window limits to need 2b reset. Radio Stations and settings are preserved. As Jay pointed out you next test for whats draining the battery. Despite you forgetting to acknowledge DVM knowledge I'm going to post a way to do this at the fuse box standby.

John

 

Here's the link:
Mm, yes this is really showing you how to read the current draw of a circuit without pulling a fuse or disconncting the battery. In case you didn't know, each of those plastic fuses has a rectangular whole on top right above the fuse blade for your DVM probes' access.

20 minutes and you should know exactly what's draining the battery. BMW thanks to Jay for explaining how to put the car to sleep for best readings.

M, questions? Just ask us.

John

 

Moderator, this question comes up a couple of times per year. I posted the original link to this video, but always have to search for 20minutes to find it :-).

Is there anyway to tag it or something so we can get to it easier? Seems like something everyone can use sooner or later. Thanks,

John