There is a lot of advice on how to get into a trunk when you have a dead battery but I could not find anything that I knew was specific to a 351 (11' Jaguar XJ). Will a trickle charger in the "cigarette lighter" socket work to get a little charge to the battery? Any other ideas? I have read what the manual says about how to address the problem and doing it scares me to death (even the manual provides a warning) which means if that is the only option I'll have to get AAA to tow it to the dealer or get the dealer come to me.

That a car should be invented that can have this problem sounds like a huge error in thinking to me. I have jumped gobs of cars in my time but who would have believed a dead batter that you cannot easily access.

Thanks in advance for your help!

 

Open the hood and remove the fuse box cover. Attach a positive lead to the vertical tab by the fuse, and connect a negative lead to the threaded stud below the box (there should be a label that shows you where it is, but you can use any ground stud). You should now be able to press the trunk release button.

If the doors are still locked, open your keyfob and remove the key blade inside it. The rear fixed part of the passenger door handle has a small cut out underneath it that you use to pry it off (forward). Then you will see a lock barrel to insert the key blade into.

 

I am still looking for an easier option. Will a trickle charger plugged into the cigarette lighter give the battery a charge or is it "dead" if the car is turned off? Obviously there is an easy way to check this but I am 500 miles away from the car. Maybe another 351 owner could check it for me by plugging in their phone when the car is off and seeing if it is getting any juice.

Thanks so much!

 

Hi Ralph,

You shouldn't connect any reverse charge to the accessory sockets on modern cars, the electronics are not designed for that and this case the fuse box is intelligent and isolates them from the battery anyway so it won't help you to open the trunk.

A brief explanation of the way battery power is handled in these cars might be useful. You typically think of three states - off, accessory (ignition position II) and engine running. In the X351 there are around a dozen different states, although only 9 are described (the rest appear to be intermediate or diagnostic states). Some of them like the accessory state are load managed to prevent them being able to drain the vehicle battery. The state and sequence of doors being opened, the engine having been run, and other factors all determine whether your accessory sockets will have power with the ignition off and if so for how long.

For example if you open the doors, plug in your phone, then close the doors and lock the vehicle the accessory power will be disabled immediately.
If you were to repeat that but turn the ignition on (II) or start the engine, then turn the ignition off before closing the doors the power would remain on for up to 15 minutes depending on the load.
If you were to remain in the car but pass the keys out the window and have someone else lock it then after the power is disabled you could unplug and reconnect the phone and the power would still be off.
You could use a multimeter to confirm there is no connection to the battery.

You can connect your trickle charger to the fuse box location mentioned above in order to unlock the trunk to get to the battery. It was designed for that purpose, and can be used for long term conditioning if desired (although you can also use the trunk for that as long as you include the BMS and do not connect directly to the battery posts).

The only difficult bit about the process is getting into the cabin on a dead vehicle as you need to faff about the key blade. Surely once you are in it is no harder to open the bonnet than it is to plug something into an accessory socket.

 

Perhaps I can make a contribution by showing a picture of the connections. Left finger grasping the positive connection. You'll also see the removed red cap. Right finger points to the place to attach the ground (next to the leaf) Baker Jaguar in Charleston SC was a big help in my understanding what is involved and now it seems simple to me.