My numbers are consistent with Ralph's 2013 XKR. I have not been using a battery maintainer for the last month and have been running alot of accessories (heater, convertible top, heated steering wheel, and heated seats) with absolutely no problems. I assume the BMS is operating normally. No problems no worries.

 

I'm reviving this thread because my AGM replacement battery failed after being installed for about 18 months. I had the battery professionally tested by Interstate. My ashtray voltage gage never read more than 13.4 and goes from 11.4 to 13.4. With the car running and a voltage meter on the battery the voltage reads 11.89. I'm not sure how the BMS works and if it is manipulating the voltage. My understanding is the voltage should read about 14.2 with the car running or at least 12.4 with a good alternator. Voltage behavior from the ashtray voltage gage has been discussed in previous posts with no concern for the ashtray gage never going higher than 13.4 and going down to 11.4. I'm wondering if my alternator is defective and caused my new battery installed about 18 months ago to go bad. I have not had the car on a maintainer this summer because I drove in at least once every week or so. During the winter the battery was connected to a maintainer. I had my battery tested because the starter turned very slowly, barely starting the car. No usual low battery electrical problems were experienced. I installed a new replacement AGM battery yesterday and the ashtray voltage gage is behaving the same with no change. The new replacement battery was fully charged and tested before installing it.

My questions are:
1. How does the BMS work? Does it stop the voltage from going above 13.4 as measured in the ashtray gage.
2. Should I take it to the dealer to test the alternator and BMS system?
3. Should I check the alternator pulley to see if the belt is spinning the alternator?
4. Should I just go ahead and replace the alternator?
5. Is everything working fine and I just got a bad battery?
6. MY14 and MY15 have different Jaguar battery specs than previous years. Interstate battery recommends different batteries also and does not recommend an AGM battery for MY14 and MY15, but suggest an AGM battery can be used for MY13 and before. Could the AGM battery I'm using be the problem?

 

To start, Your ashtray gauge is not measuring the voltage at the battery. To answer your questions
1. BMS does manage the flow of electrical current and available potential to the battery. It is roughly the same technology as included in any modern day battery charger/maintainer. The workshop manual for your car clearly lays out pinpoint tests. Either you or the dealer should follow this process.
2. The pinpoint tests cover the entire charging system
3. of course…. but I suspect the idler pulley is keeping it suitably taunt. You would hear it squealing if there was an issue.
4. Your money…. but before performing the tests??
5. Who’s to know without performing the tests??
6. I suppose you could take the word of the battery manufacturer…. I’d take the word of the car manufacturer.

Lastly, if you are driving the car on short runs, you may mot have fully charged the battery before shutting the engine down. Over time, this would take the effect of reducing the potential contained in the battery. A battery stored in a depleted state may or may not accept a full charge.

 

Had essentially the same thing happen 2 years ago with one of my other contemporary JLRs. Voltage at the battery was constantly all over the place from 11 volts to over 17 volts. Main dealer insisted BMS makes it impossible to monitor voltage at the battery. But what I know of automotive electrics systems, regardless of BMS, voltage SHOULD be consistent. So I replaced the alternator myself and magically the voltage stayed steady at 14.2 +/- 1 volt every day I tested it AND other electrics issues went away.

 

Wonderful to see an old thread where I was a complete jerk to Barnsie. Not much to add except since my last post in this thread, I added CarPlay so I had to give up my touchscreen gauge display and I replaced it with the same ashtray model you have @DGL . I'm consistently reading 14.0 -14.2 on it. I know you aren't full on DIY but to guy's point #3, the belt can be suspect and as you almost always hear squealing with a loose belt, easy enough to check by just finding the longest length of the serpentine belt and push inward at the center. There should be no more than 1/2" of movement. But again to guy's point, in cool or cold weather, you will most likely hear squealing. If the belt is OK, I'm in agreement with jahummer. Suspect the alternator and test the output there.

 

The alternator is accessible from under the car. Should I put the multimeter on the alternator terminals to test it when the car is running?

 

Sorry I can't advise. When I look at the wiring diagram, you're MY setup is different than mine. Someone with experience in 2012 onward should be able to weigh in.

 

You can, very carefully, one to earth, chassis, and other to the terminal on the alternator but be careful not to short it out. But I found going direct to the battery cables was sufficient. Like I said the voltage should be constant from the alternator at idle. Squeaks and squeals I’ve found to be common and due to failing pulleys, there’s 9+ I think?

 

Made an appointment with the dealer to inspect the electrical charging system, Friday. I'm experiencing no electrical problems except for the new AGM battery going bad after 18 months. Another new AGM battery installed. Even with the old bad battery I experienced no unusual low battery problems; however, the battery tested at 11.89 volts in and out of the car. I just want to know if everything is working properly (BMS, alternator, belts etc).

 

keep us posted please

 

Hope you’ve better luck with your main dealer than I did. As I said before it’s pretty simple, if the alternator’s not putting out 14.2 volts +/- consistently, it’s done….

 

If my alternator is shot is a remanufactured or aftermarket alternative a good solution or should I stay with branded Jaguar alternator?

 

I'd stick with the Genuine OEM match, Denso, I think it was. Got mine from RM European for about 90% off the main dealer's price....

Here you go, less than $200 and great people to work with

https://www.rmeuropean.com/Products/...G11-V5522.aspx

 

The dealer could not identify anything wrong. They said the alternator was generating sufficient amps under load and unusual events where noticed with car asleep draining the battery.

​​​​They first had to charge the battery for 2 hours because it was low and they could not do any proper testing on a low battery. The new battery was install a couple weeks ago, fully charged and tested. Also the car was driven every 3 days for about an hour. The tech said there could still be something wrong with the alternator like the clutch not engaging when it should.

​​​​​​They also reset the BMS. I did this myself with last battery I installed.

It looks like I'll need to keep the car connected to a battery maintainer when not being used. I might just order a new alternator and install it to see if it will make a difference if I'm allowed to return it.

 

Very similar experience to what happened at the main dealer. It’s been two years nearly since I replaced it with no further issues. Get the one from the link I posted above, it’s the same as supplied by JLR for a grand less.

 

I'm in Canada. I'll need to pay $80US shipping then duties and finally sales tax (15%) on everything. My cost would be $485CDN at the door which may be cheaper than buying local. I do some more digging.

 

I bet once you install it, even if it does not help the issue you will not really want to go through the process of pulling it out.
Of course ymmv but, although not difficult it is time consuming...especially if you don't have access to a lift.
Also, although my car does not have the 'double lock that locks the doors on the inside" I have measured far less draw on the battery if the lock button is depressed twice.
wj

 

You' re right. I always do a double lock. The dealer tested for any intermittent electrical drain.

 

Where do I find these pinpoint test? I can't seem to find it in the manual.

 

I couldn't find one either - according to the wiring schematic the jump start post is directly connected to the alternator via the starter so that would be the actual alternator output voltage.

PRINCIPLES OF OPERATION
The output voltage required from the generator is calculated by the battery monitoring system. For additional information,
refer to Battery, Mounting and Cables (414-01 Battery, Mounting and Cables, Description and Operation).
The battery monitoring system signals the required voltage to the ECM via the CJB (central junction box) and the instrument
cluster. The ECM then transmits the required voltage on the LIN bus connection with the voltage regulator in the generator.
The output from the generator is supplied to the battery through the main battery positive cable.
The ECM will over-ride the voltage value requested by the battery monitoring system if it detects a fault in the generator.
The ECM also signals the instrument cluster to display a warning message if it detects a fault with the generator.
For additional information, refer to: Instrument Cluster (413-01 Instrument Cluster, Description and Operation).