I recently had some electrical issues that may have been caused by a bad battery, but I feel like this does not fully explain the issue.
I was fine until I drove through some rain, and then the electrical system started turning on and off. The central display turned off, and among other warnings I got a notification that the traction control had turned off. I managed to make it to my destination and the rain stopped. When driving back after the rain (although the roads were still damp), the car seemed fine for the first half of the trip, and then the issue reoccurred, and since it was night time my headlights also blinked on and off, sometimes rapidly. So, I stopped at a gas station to investigate, and when I turned the engine off, the car completely died on me. Nothing electrical worked, including the glove box latch, trunk latch, and windows (which is needed to close the door). Eventually someone asked if I needed a jump, and I agreed, using the jump points under the hood. This turned the electrical systems back on and I was able to start the car, and from there made it home with no problems.

I put the battery, which was only 18 months old from Autozone (Duralast), on my nice CTEK charger designed for AGM batteries and reconditioning, and the red warning light came on that indicated that the battery might have been sulfated. I was able to claim the warranty on the battery at Autozone (even though their simple tester claimed it was good at 85% or something). The new battery charges OK but I have not installed it yet.

My question is, does this problem sound like something that is just the battery? I am unsure why this only cropped up during the rain, and it made me believe that it was a wiring issues somewhere. This might also explain why the battery had gone bad after only 18 months? But, I am not sure how I could really test for an intermittent problem like this.

My second question, now that I am thinking about it again, is it advisable to remove the secondary battery for Eco mode? My understanding is that the electrical system switches to this battery when stopped and the main battery restarts the car, then it switches back when driving. I have heard that it is fine to disable or completely remove this battery with no ill effects other than disabling Eco mode, which I don't want anyway. However, I was wondering if there were instructions for if I wanted to fully remove this battery and save on some dead weight, rather than just remove the ground cable. Might eliminate one source of electrical problems, too.

Thanks.

 

I can't help you with your first question (main battery) but I can offer some advice on your second question (removing the secondary battery).
Yes it is perfectly OK to remove that battery and doing so has no effect on anything other than to permanently disable the start/stop system.
If anything it might improve the health and/or prolong the life of the main battery, my main battery is still going strong at nearly nine years old now although I do connect up a battery tender whenever the car is parked in my garage.
The secondary battery is easy to remove, just unbolt the cables and the mounting brackets and remove them from the car, I did exactly that a few years ago.
Only one tip/trick - one of the bracket mounting bolts is tucked up under the rear trim panel and you need a "wobble" extension on your socket wrench to get at it.

 

First, the eco battery can be disconnected and/or removed with absolutely no effect on any system except the irritating stop/stop, which, happily, ceases to annoy.

Second, your main battery may be faulty but you may also have bad connections at the battery itself or at the negative cable connection on the floor of the trunk. A faulty or intermittent connection would explain the symptoms your car has been exhibiting.

 

The CTEK unit has buttons to choose either a conventional battery or an AGM battery. Did you select the correct setting for the old battery and to charge your new battery ?
You were/are wise to fully charge a new battery before installing it. I put a new battery in my Mazda CX 5 not long ago and upgraded to an AGM type. I put it on my CTEK unit before installing it and it took almost 8 hours before the indicator lights showed it was fully charged.

Yep get rid of the secondary battery and check all the connections and I'll bet you'll be OK.

 

Yes, I selected both 'AGM' and 'recondition' (and also 'car' as opposed to 'motorcycle'). For both the old and new battery. Old battery I tried three or four times and it never got past step one. Still wondering how it wore out so fast, perhaps Duralast is just a crap brand.
It's this charger

 

Thanks. Still wondering how the car completely died at the gas station, and then seemed to work somewhat afterwards. After getting home that day I have not driven the car again, but the door locks and trunk and such continued to work until I took the battery out.

Any other tips for removing that secondary battery? There are a lot of cables over near it, and I'm wondering the best way to cap off the unused cables, etc.

 

No other tips.
Once you remove the battery and the upper mounting bracket you are left with the negative/earth lead (black) and the positive lead (red), and you remove both by unbolting them at each end. I left the bottom mounting bracket in place as I couldn't see how/where it was fixed to the floor of the trunk/boot.
This leaves two large red cables on the floor of the trunk/boot near the mounting bracket, don't mess with them and leave them in place, they have nothing to do with the secondary battery.

 

That's the favourite!

 

So, I managed to remove the auxiliary battery. That required first removing the module in the middle read of the compartment (I think it is for the active suspension), then I removed the entire battery assembly. I had to put that on my workbench to remove the actual battery and battery cables. What remained were the main bracket and upper bracket, as well as an attached module that the two red wires go to. I suspect this module is just to switch which battery is controlling all the secondary electronics during the start/stop event. I suspect this module is now unnecessary if I bridged the two red cables to each other, but I didn't mess with any of this right now. I had to put the upper bracket back on because it is required to bolt the assembly back into the trunk and it also is where the active suspension module is bolted (I should attach pictures at some point)

The secondary battery itself was 100% dead, which isn't too surprising, although I remember the car going into eco mode at a light just a couple months ago, so that's odd.

Additionally, I took a look under the car to see if there was any obvious wiring damage (can't see much, so I dunno). And finally, decided to put the engine cover back on, because I read that rain getting into the hood louvers could cause issues, and it looks like the engine cover might actually shield things a bit, despite hearing previously that the cover was completely useless (I had made a special mount to display it on my wall, even)

 

Unfortunately, despite a brand new battery, I had the car die on me again. It was parked outside for maybe 14 hours on a day it got up to maybe 90 degrees. Car turned on, failed to start, and then was totally dead after the failed start attempt. What's worse is that the standalone jump pack I carried for this situation apparently did not have enough power to start the car either. Luckily, a friend was nearby who was able to use his own jump pack which worked, and then I was able to make it home OK (and nothing cut out while driving this time). So, I must have some sort of parasitic current leak somewhere. I realized that one candidate was the USB charger I had plugged into the center console, but I checked that and it didn't seem to be drawing any current with nothing plugged into it charging. I have now acquired a 'fuse buddy' which helps to test individual circuits in the car by replacing the fuse with a wire loop, as well as a DC clamp meter. So hopefully I will be able to track down whatever is causing the issue.

Is there any circuit that is particularly known for causing a parasitic draw? If there is a good place to check before I start looking at every single circuit, it might save some time.

Secondly, I was wondering if anyone had a recommendation for a jump pack that works well? I have the 3.0 liter V6 S model (new oil change too).
The one I had that failed was this https://www.oreillyauto.com/detail/c...ter/ss02/55002
Claimed 1000 amps which I thought would be enough.
My friend's was apparently this Claims only 500 amps, but it worked. I am hesitant to keep a lithium ion pack inside my car because it seems like a fire hazard, but if it's the only thing that will work I guess I might relent. I also keep regular jumper cables but I can't always rely on those.

 

Make sure you check the integrity of the connections of the main power wire (large and RED) that carries battery voltage to the engine bay.

It is situated along the bottom of the car, just to the right of the exhaust.

 

Is this the thick gray wire going into the bulkhead? I haven't checked that specific connection yet. It was not visible underneath the car either.

 

There are multiple main grounding points on the car and a failure of any one of those could result in the symptoms you're seeing. Definitely worth checking to make sure they are all tight and not corroded.

 

I'll have to check for a list of them, although I kinda doubt there is much corrosion.

In the meantime I'm considering a NOCO brand jump pack. They seem to be recommended pretty often.

Was also considering a Jaguar specific OBD reader. (I am aware of the problem with the OBD port that can drain batteries. I haven't connected one in a while so I can't blame the recent failures on that.)

 

There are two TSBs that may be contributing to your intermittent faults. You may want to check them out. One refers to loose connections on "+" cables, the other deals with poor "-" connections...either one could produce intermittent faults that you describe.

 

Oh, that's good info, thanks.
I checked the individual bolt in the battery junction box. Didn't seem to be loose but I torqued it anyway just to be sure.

As to the other TSB that replaces all the earth studs, well that repair looks to be beyond what I would attempt myself, but the three locations I could find seemed to be free of damage/corrosion, from what I could tell.

In the meantime, I bought a NOCO jump pack rated to 1750 amps, which will hopefully be sufficient, and I intend to borrow my friends snap-on brand obd reader to check for any special Jaguar codes (I heard there is a recommended reader for these Jaguars but I'm not sure if it is still necessary in the year 2023).

I'll also have to buy some more plastic panel clips for the access panels under the hood, because I believe I lost two of them in the engine bay...

 

I have one of the NOCO battery packs. They work well

First step before you go chasing all sorts of issues. You need to know if you have a battery drain issue or a poor earthing connection issue. So - when the car fails to start, what is the voltage across the main battery terminals? If it's good (should be around 12.8 ish for a well charged AGM) then it's not battery drain, it's a connection / earthing / starter issue. If it's low then it's battery drain or a fault with alternator

And when the car is running what is the voltage across the battery? Should be running over 14V when alternator is running

Finally - when you close and lock up the car does the red warning triangle go off after 10-15 mins? If not that's your issue (modules not shutting down)

 

I think it can't be the battery (despite also having a bad battery previously)

I just had it happen again, in my own garage this time. Turned on the car, then when trying to start the, the car died on me.

So I popped the hood and checked the voltage on the jump point up there. 3.8 volts. Then I hooked up my new jump pack, and before starting the car I popped the trunk to check battery voltage. 12.7 volts.

Then I successfully started the car with the jump pack. When I removed the jump pack the engine didn't like that and revved a bit more before settling back to normal. I also noticed the flickering headlights again this time, until the engine settled into it's normal idle speed.

At this point I checked the voltage on the front jump point again, 14.3 volts. And the battery voltage again. Roughly the same around 12.7 volts. I assume the battery and jump point should have the same voltage more or less?

Anyway, I backed the car out for another project I needed the garage for, and it immediately died upon shutting it off again.

So yes, I think there must be something wrong between the trunk and the engine compartment. Not sure where to go from here except to take it into a shop/dealership.


Edit: And now, pulling back into the garage, the engine did not even remain running after unplugging the jump pack. Does that make sense at all? I had to leave the jump pack connected and the hood halfway open in order to pull the 20 ft back into the garage. The situation has degraded pretty quickly.

Edit 2: So I realized that the whole frame of the car is not directly tied to the negative battery terminal, but goes through this little "battery monitoring system" thing. The whole body of the car is at about +9V relative to the negative battery terminal, hence only seeing ~3 volts at the front jump point. Not sure what to make of this, yet.

Edit 3: I'm gonna feel like a real idiot if this was the only problem, but I noticed the voltage difference was across the battery clamp terminal itself, so I cleaned both terminals and cables with a wire brush and then isotropyl, and that fixed the problem for now. The terminals LOOKED clean, and I swore I had checked for continuity here, before. I might blame this on some "battery terminal & cable protector" grease that I had applied almost two years ago. I'm still not satisfied that this is the only issue, but I'll keep the jump pack in my car and see if it fails again.

 

I've had seemingly tight battery terminals develop high resistance after replacing a battery (not, on a Jag). The cause was that many replacement batteries have slightly smaller battery posts. So the cable terminals look tight, but can develop a high resistance over a period of time. In my case, 6 - 8 months.

If you think that is the issue, you could buy a pair of battery terminal shims...only a few $$. Local auto parts stores carry them.

 

Carbuff2 makes a good point. I had a Nissan 370Z with a replacement battery that was a couple of years old and one day it wouldn't start. I checked under the hood, wiggled the cables that were attached to the terminals and the car started. Under closer examination, although the clamps were tightened fully the one on the positive terminal was still a bit loose. I made a shim out of a tin can to get me to the auto parts store and bought a set of those terminal cap shims. I installed both when I got back home and never had another problem. It was odd that it took so long before I had a problem. But the terminals were definitely smaller than the minimum inside diameter of the clamps and the shims were an easy and inexpensive fix.