I have a 2004 Jaguar XJ6 that ran great until I let it sit for 5 months and battery was Dead (11.4 volts). So I removed the battery to charge. Following recharging to 12.5V, I re-installed it and tried to start but it would not even crank. All lights and radio works but steering stays locked and the anti theft light on the dash flashes quickly with the key turned on. The battery in the remote seems OK since I can open and close door locks with remote. I moved shifter from Park to Neutral but no difference.
I have a feeling it's a simple fix for someone who had the same issue, but I can't figure it out. Any advice would be welcomed.

 

Not sure on the X350,

BUT

On my both the X300, and both the S Types, when replacing/reconnecting the battery for any reason, I used the key fob to "lock, then unlock" the car.

This appeared to give all the cars the warm and fuzzies, and all was good in Jaguar Land.

No idea on the X Type yet, had no reason to play with the battery.

Worth a try.

 

Your battery is providing insufficient amps to crank the engine. If you recharge to 12.5v static then the battery is only half charged. When you load it up by cranking the voltage will drop way below 12v thus the systems will not operate. The battery is likely very weak after standing and sulphating up so may never be able to be charged fully. I suggest a new battery will cure all your ills or get a decent charger to charge it over 12.75v. If you check the battery voltage when cranking you will see what I mean. These cars need a decent battery to run properly and its a simple fix.

 

+1

Get a new battery and save yourself a lot of grief.

Graham