Hi everyone! Does anyone experienced battery power loss until is almost flat dead while the car is off for at least 3 days? This has being happening for a few months now. Any advice please. Thank you very much.

 

There is obviously something still live with the ignition off. One of my rear seat courtesy lights stays on now & again which flattens the battery. Try removing the bulbs in the boot & under the bonnet in case one of them is staying on & also check all other lights.

 

you have a parasitic draw on the system. You will need to meter the battery draw at the battery terminals, while pulling fuses from the fuse boxed...one at a time.

Do you have a meter?

Do a search in the XJ40 archives with the words "parasitic draw" as part of the search parameter. Myself and others have written in detail how-to find the circuit causing the problem.

 

I literally just went through this with my XJS. It turned out to be a bad battery. Darndest thing. I could charge it, car would start great. But let it sit overnight, and it would be down to something like 7.3 volts overnight, but never flat dead. After spending a lot of time tracking down everything else, I took the battery and had it tested. Exactly my problem.

 

My apologies for the delay , thanks to all of you for your help. I'll get a multimeter this week to start performing the troubleshooting as told . I am sure it will be an interesting and valuable learning time. I will post again with the results of my search.
Best regards,
Alberto