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Discussion Starter · #1 ·
Had this warning almost a yera ago and ended up had 12v Aux Battery replaced for my FE with 30000 miles then. Now after $15000 more miles, got the same warning again yesterday. Cannot get an appointment until Feb 1. keep my finger crossed can drive with caution until then.

The WattCat is showing Aux bettery is at 13.9 v and TCU battery is at 90%. Deraler said since the bettery is less than one old, it might be something else like wiring harness. They only changed one battery last time. Could it be the other one (I also hear there is the thired on on the back)?

Any adivise? Thanks.
 

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The WattCat reading (API data) is only the startup battery. The small auxiliary battery may have failed or it's the wiring harness problem. It is located in front on the left side of the car.
 

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Discussion Starter · #4 · (Edited)
The WattCat reading (API data) is only the startup battery. The small auxiliary battery may have failed or it's the wiring harness problem. It is located in front on the left side of the car.
Just measured, the battery in the front drive side is at 5.4v.Won't be able to start, just brings up all kind of warnings. It is the battery the dealer replaced 11 months ago. What is the possible cause? Should try to get it jumped and keep driving until the appointment?
 

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See the bold warning in the first post of What to expect and do with 12V battery failures - pre-MY21

If it is the same battery, then either the battery is defective, or software updates are needed, or the power supply distribution box has developed a fault. This should be covered by warranty unless you've passed 5 years/60K miles.

Are the connections to the battery good and tight? Is the ground cable tightly secured to the body (under the trim panel towards the charging port).
 

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Discussion Starter · #6 ·
I was able to open the hood and measure the battery in the drive side (only 5.4v). Is this the one you refer to as the starter battery? This battery is also used for other Jaguar cars and are readily available at my local dearler. The display does light up with all sorts of warnings but I do not think the car is acturally started. I had a notice of software update and oked it. Not sure if it has something to do with it.

Can the car get on the flatbed tow truck or need to jump it first? Thanks.
 

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The large battery is the start up battery.

A failed auxiliary battery will not supply power to the parking locking. You can release that manually it.

If the car stays powered up (not in READY mode), you can electrically release the rear parking brake with the switch inside (near driver knee). You might also put your foot on the brake and press the N to see if it will go into neutral. That should get it so that it could be pulled onto a flatbed tow truck. Get out the towing eye from under the cargo area floor.
 

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Discussion Starter · #9 ·
Thanks for the information. This can be helpful for getting the car to the flatbed tow truck.

However, I still not total clear about which is which in terms of battery. Starter battery, Aux battery, TCU battery, then the dearler showed a picture about a battery in rear?
 

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Thanks for the information. This can be helpful for getting the car to the flatbed tow truck.

However, I still not total clear about which is which in terms of battery. Starter battery, Aux battery, TCU battery, then the dearler showed a picture about a battery in rear?
In pre 2021cars, the Startup is the big battery and the Aux is the smaller one (under the hood).
 

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TCU battery is in the rear of the car inside the TCU. It should not need replacement. That is only as a back up to the TCU.
 

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Discussion Starter · #13 ·
I can lock and unlock doors, open and close hood and rear gate, display lights up (with all kinds of warnings), lights are on, power seats can be adjusted but just won't start (fleashing P, cannot put into R or D).Wattcat show Aux Battery at 13.9v and TCU at 90%. Which battery is bad? Can the car be jumped to drive? Do a level 1 or 2 charging will help?
 

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The SMALL battery is bad. You might be able to jump it to get it into neutral, but don't count on it working properly after removing the jumper. Did you try getting it into N?

A 90% TCU charge is the normal value for a fully charged TCU backup battery. It is not the problem.
 

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Discussion Starter · #15 ·
The SMALL battery is bad. You might be able to jump it to get it into neutral, but don't count on it working properly after removing the jumper. Did you try getting it into N?

A 90% TCU charge is the normal value for a fully charged TCU backup battery. It is not the problem.
There is the small one located? They changed one on the driver side 11 months ago, the big one? So now the small one is bad, too. They really should change both batterys, right?

I also checked the driver side one with a meeter it show 5.4v. Maybe I reading is not right.
 

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Discussion Starter · #16 · (Edited)
I think I was mistaken. See if I got it right this time.

1)The smaller one (the Aux bettery) is on the driver side and this is the one got bad (only 5.4v) in my case. This one may not be readily avaivable. I am worried about it may take long time to get the battery. This one is not monited by WattCat.
2) Once the car started, the Aux bettery is no longer needed.
3) The bigger one (the starter battery) is on the other side, which is the same one used by other Jaguar cars so the dealer more likely have it in stock (it is in my case). I think that is the one replaced by the dealer 11months ago in my case and it is still good (measured at 14.4v) (code JDE32902)
4) TCU battery is the third battery in the back. It is not an one to be concerned.
Anyway, I was able to jump the smaller one and back up to the tow track. In fact, when arrived at the dealer, I was able to start it again and drive to parking spot.

So the dearler really should reaplace the both batteries last time or placed an order for the smaller battery

Am I right?

Thanks.
 

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JDE32902 is the smaller battery. It is the one you measured with low voltage and jumped to get the car started.
T4K4462 is the larger battery.

The smaller battery has been used in Jaguar and Land Rover vehicles going back at least to 2012. It is used as a start/stop support battery. It shouldn't take too long to get a replacement. Even if the dealer doesn't have one on hand, a JLR warehouse of parts should have it in stock unless they are really bad at logistics.

As I posted above "If it is the same battery, then either the battery is defective, or software updates are needed, or the power supply distribution box has developed a fault." Those software updates could be to multiple modules.
 

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Discussion Starter · #18 · (Edited)
JDE32902 is the smaller battery. It is the one you measured with low voltage and jumped to get the car started.
T4K4462 is the larger battery.

The smaller battery has been used in Jaguar and Land Rover vehicles going back at least to 2012. It is used as a start/stop support battery. It shouldn't take too long to get a replacement. Even if the dealer doesn't have one on hand, a JLR warehouse of parts should have it in stock unless they are really bad at logistics.

As I posted above "If it is the same battery, then either the battery is defective, or software updates are needed, or the power supply distribution box has developed a fault." Those software updates could be to multiple modules.
Thanks. They do have the same battery replaced last time so the question is why it got bad in 11 months. I remembera massege poped up saying an update is available recdently and I clicked yes. Not sure if it has something to do with it.

What about the bigger one? Which one (or both) are likely/often got bad? Should I ask the dearler to replaced the both batteries if possible?
 

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The update was either Infotainment S22A or TCU update 20.2. Neither one should have any relevance to this situation.

The dealer will only replace parts as needed to repair this situation and have it covered by warranty. Anything else is on your wallet. There is nothing in your description above indicating a problem with the larger battery.
 
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