1996 xj6 battery drain

Hi, new member here.

So, my daughter bought a 1996 xj6 last year and we have been slowly working out the bugs.

Our latest issue is a battery drain problem. I installed a new battery, but it seems to drain down over time. Granted, she isnt driving it daily and sometimes goes a week or two (maybe more) without starting it, despite my constant reminders.

Anyway, it charges fine but always seems to be dead after sitting for a while. I suspect that the alarm system may be responsible, but i have no real reason to suspect it other than when it chirps, it starts. When it doesn’t chirp, no start.

I have searched in the trunk for a backup battery but haven’t found it. I honestly can’t tell if its under a seat, my head is too big to fit under there…

Anyway, i was curious if anyone knows if it has a backup alarm battery and where this might be located.

Also, I guess i just learned that this is also known as an x300? I will search again using the x300 model and see if i get more results.

Any help is appreciated, thanks!

Hi Chris welcome to the forums, I see you have found the correct site.
First thing you need to do is perform a draw down test on ALL the systems in the car, there are about 5-6 fuse boxes and you need to check each fuse in turn.
When checking the fuses in the boot you can fool the computer into thinking it is closed by tripping the catch with a round bar or screw driver.
Disconnect the neg battery lead and place a digital multi metre in series.
You need to let the car ‘go to sleep’ before pulling each fuse to see if the current draw drops, you are looking for a draw of a few milli amps from memory.
If once the car is asleep and the current draw is in the millamp situation then that would indicate that there is’nt a parasitic draw and its probably just the length of time between uses.
I have a X308 XJR and have to keep a solar panel connected as its not our primary car.


Thanks for the reply. I did another search
and found references of 30 to 40 mA being normal draw after the 15 - 20 minute wait for “sleep”. I will have to check this as I haven’t done this test yet.

I should also add that i haven’t found any lights staying on that may be drawing power.
In fact, the glove box, trunk and hood lights don’t even work when its running, lol. I do however, have the red occasional flash from the dash when it’s off which i believe is the alarm light.

I had it on the charger tonight and then fired it up, runs fairly well. The alternator is putting out good power and I dont think she has had a problem when she runs it more often, so it’s not an “overnight drain” like some I have read about.

Anyway, ill throw a meter on it in the next few days and report my findings.

Thanks again!

Ok, so i finally had a chance to fully charge the battery and do some testing. Initially i had an amp draw of .58A, which seemed pretty good.

Then i finally found the trunk lights, they were inside the trunk lid behind the carpet! After fishing them out and unplugging the bulbs, the amp draw dropped down to .15A! Which almost seems to good to be true…

If the draw is really that low (.15A) then i can’t understand how it draws enough current to drain the battery completely over 2-3 weeks. The only thing I can think of is a disconnected power lead to something that occasionally touches ground. Previous owner had a 6 disc CD changer and some other extras but removed them before the sale. I taped up a push-on connector for one of these that i found in the trunk area before testing.

I havent found anything else yet…Any thoughts on what I might be missing?

Some math required here. Your number of 0.15 amps is not too good to be true. It is 150 milliamps, which is at least three times what I think it should be.

My experience is with a 94 XJS which I think should be somewhat similar. Seem to recall I got 50 ma as a repeatable number.

Hope this helps.

You know, now that makes sense! I dont know why i wasn’t thinking about that the correct way, I certainly know better, just being a tool today I guess.

That is good news ultimately because it explains that i do still have a drain and i just need to find it.

Thanks for pointing that out…sometimes it’s the obvious details we miss and someone else has to point them out…

Ok, so the drain seems to be coming from fuse#5 from the terminal post in the rear fuse box. Its a 10amp and, if i have the correct diagram, it feeds the BPU.

Now i just need to figure out what that unit does and if there’s a way to fix it or if i just need to replace it…

Ok, after researching this a bit, the BPU (also known as BPM) controls all the lights, seat heaters, wipers, etc. etc., so it could be any circuit related to those things or if I understand this correctly, it could be the BPU itself not shutting off power to one or more of these circuits.

I found a used BPM on ebay and ordered it this morning, so i at least have a spare if I muck this one up,lol.

I also read about the ignition switch having a horizontal function in addition to it’s rotary function and that can cause certain circuits to remain on when the key is out. I will have to check that when I get more time.

Im sure that the majority of members on here know all this already, but I am putting all this info in for the next “newbie” like me that comes along.

Also, i have had much better luck with the search terms “x300” and “BPM” than with “xj6” and “BPU”

So, I have great news! The new BPM arrived and it was a perfect match, made just one month after the vehicle.

However, before I installed it, I did something that I should have done from the beginning: a hard reset of the BPM. Since I had to disconnect the battery anyway, I clamped the two cables together and left it for about 30 minutes and tested again. I had .03A!!

I put the cables back on and started the car, ran it for a while and then shut it down and tested again after the 15 minute wait for sleep. Still at .03!

I did this about 4 times and got the same result every time. Then my daughter took it to do some shopping. After she came back, I waited again and tested. Again, .03!

I suppose I should have done this first, but
I don’t mind having a backup BPM on hand for the future and the price was decent, so I have no regrets.

Thanks to all for the help. I will keep testing periodically to make sure the condition doesn’t return, but I am hopeful for now.


Never thought to suggest a hard reset, great to hear that it might have been as simple a cure as that.

My 96 spends 5 or 6 months a year jacked up on blocks as it is my “winter car” in Florida. If your daughters usage becomes more infrequent a small battery tender may be helpful, I use them on both my summer and winter rides with good results.

She had her first accident today, it was minor but I will be spending my evening trying to figure out how to reattach the front bumper.

This is her first car and she just got her license, so I can only hope it was a learning experience.

Also, I should mention that yes, she has had the car for a year, but just got her full license. She knew she wanted a jag, and saw a good opportunity. She has good taste at least!

Great tip on the battery tender, but I am hoping she drives it more frequently in the future. If she drives less often, I will probably look more into the battery tender. Thanks!