2000 XJ8, 124k miles. It's my wife's car and seldom driven. I had a problem last year with a 2-year-old AGM battery going dead after being parked for about a month. I replaced the battery with a new H8 AGM and since then I've been keeping the car on a tender (CTek 0.8) full-time when it's not in use. However, even with that (and a now 1-year-old AGM...) the battery up and died over the weekend. Yesterday I went to get something out of the car and it wouldn't unlock. Manually keyed in the drivers door but the other 3 doors and trunk remained locked. Tried to start the car and nothing. Not even a click... Upon opening the trunk my CTek was throwing the red "battery error" light. I swapped it for my CTek 4.3, which has a recondition mode, but after a little while that one threw the error light as well. Both tenders work perfectly and are in continuous use on other vehicles.
This morning I tested the battery at work and it tests at 10.45 volts and 6 CCA. I can get a new battery under warranty, but obviously there is something going on with the car. I feel like one of the computer modules is remaining active 24/7, but how do I figure that out? And if that is the case, how do I fix it?
TIA
Steve
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Hi Steve,

It definitely sounds like you have a parasitic drain. The classic way to test for this is with an ammeter or a digital multimeter.

The basic process is something like this:

Turn off all vehicle electrical loads that can be disabled (headlamps, climate blower fan, radio, etc.)
Turn the ignition off
Close the hood/bonnet
Close all four doors or use a screwdriver to push their latches into the closed position so the doors can remain open
Disconnect the battery negative cable/lead
Set the ammeter to a high amperage range (minimum 10 amps, 20 amps is better)
Connect the ammeter or multimeter leads between the battery negative cable/lead and the negative battery post
Set the ammeter outside of the trunk/boot and carefully close the trunk/boot lid, taking care not to pinch the meter leads
Switch the ignition on (do not crank the engine), then switch the ignition off
Lock all doors with the remote
Monitor the current draw and allow all the electronic models to enter sleep mode; on an X308 this may take up to 60 minutes
After 60 minutes, observe the quiescent current draw; it should be approximately 30 milliamps (0.030 amps) or less; slightly more is probably acceptable

See the attached Battery Care manual for more testing details. Also, see the great troubleshooting guide by our member avt007 (Rob) at this link:

X308 Charging/Starting Troubleshooting by avt007

If you find that your quiescent current exceeds 30 mA after 60 minutes, let us know and we'll try to help you pinpoint the offending circuit.

Cheers,

Don

 

Pretty much have given up on worrying about the 30ma quiescent drain because it mostly reads that when the car 'goes-to-sleep'.

I keep 5 running Jaguars (3 X308 sedans and 2 X100 4.0 SuperCharged conv) and keeping up with the batteries is a challenge.

Some of them keep a battery up for a month or more but some discharge less than a month.

I simply keep a 10mm wrench in the boot on a strong magnet next to each battery.(wrench stuck to the magnet)
I disconnect each battery if I anticipate a non start and drive in the next few days.

Works for me but the trip odometer and clock become inaccurate.

Older cars never seem to give trouble but the electronics and modules of the later cars??????????????????????

 

I think the car should also be locked via the fob to cause the systems to start going into the sleep mode. It is simpler if you push the boot lid latch into the closed position so that you can keep it open and keep the multimeter in the boot. Close all doors and lock the car.

 

Thanks for the reminder, M., I added Lock all doors to the list, and your tip to keep the trunk lid open is well noted.

Cheers,

Don

 

I have been away for a little over three weeks thus not starting the Duchess during that time.
I jumped in and turned the key and even though there was SOME lag in starting, it turned over
a few times then started without issue, so there is some parasitic draw there. I suspect that
many of the control modules require current to maintain recent information in order to coordinate
that information. I am glad I opted for a high end AGM battery!

 

I'll have to check the multimeter thing next opportunity I have to play with the car. My key fob will only lock the car, so that's how it always gets locked. For whatever reason it won't unlock it -- only lock. Also, I'm waiting on parts in the midst of replacing the driver's door so right now that harness is unplugged. Guessing it needs to be plugged in again before I try and test anything....
The glovebox has always been somwhat stiff about latching when I close it -- kind of have to push it shut and then hold it there for a 2-count while the latches catch. Lubing it didn't help. So I wonder if it's not closing enough to turn the light off -- have to check that
Thanks
Steve

 

As noted, with a smart phone, you can easily check to see if the light is going out when the glove box (or trunk/boot) is locked. But, given the work you are doing in the door, you might look for a broken wire grounding out and draining the battery.

 

On some of my cars the glove box latch on the left side seems to be a bit slow to react and I must be sure that is closed and not partially open on the left side. ( you might see the light if it's a bit dark out) That will surely drain the battery. Also, if I have not started the cars in about three weeks they are slow to crank up so something is draining the battery a bit. Fortunately, our cars are the daily drivers so we don't often need to use the jump box.
Lastly, I have one of these on all my cars. It's easier than disconnecting the battery cable and I always open the switch when fooling with something electrical on the cars. I find that if after tightening the knob up, I turn the key to the pre-start key position for about 20 seconds, then hold the pedal to the floor for maybe five seconds, let up the pedal, and start the car, it starts without going into a high RPM as it's re-learning the TPS position. (Learned this on the Jaguar Forum where I learn everything important...)

You can get these just about anywhere.....

 

That little glovebox light will stay on if the microswitch isn't shut off. so that could well be a drain. You can get refit movement by adjusting the hinge screws for a better close.
Steve, with your key fob, locate some isopropyl, brake cleaner etc and crack it open, get a Qtip and soak the micro switches with the fluid (batteries out) then mop it up with kitchen roll, repeat if needed. You should see crud come loose. Once dried out replace the batteries and see if it unlocks too.
Hope this helps!

 

Those battery cut-offs are very handy. On an X308, it is prudent to be sure your trunk lid lock operates with the key before you close the trunk lid with the battery disconnected (either intentionally or unintenionally). Otherwise you'll have to apply power at the false bulkhead stud to get the trunk open again. On many of the X308s I have worked on the trunk lid locks were gunked up and would not turn with the key. Cleaning the lock and making sure it works is good routine maintenance.

Cheers,

Don

 

Yes sir...trying to get into one of these with a locked trunk and the key not working and no
unlock from the fob or dash is very frustrating. I have read the tales of woe from forum
members who have had this happen.