The 4+ year-old battery on my XF apparently gave up the ghost the other night resulting in the car sitting completely dead for several hours, then another hour or two with the battery out while I drove all over town (in my Toyota) looking for a suitable replacement battery.

Once back up and running, the performance and response doesn't feel quite right.. Does leaving the battery out for an extended period result in a reset ECU ? (the car has a few performance modifications including a remapped/tuned ecu)

 

Could be, but the ECU is usually hard coded. Other things may need to be reset also. Have you tried the auto up/down windows yet? Seat memory?

 

I am wondering about the ECU 'learning' part, that takes 150 miles or so to 'relearn'?

some items were erased like the time on the clock and the trip-milage, but other things like radio stations were still there. Also had to hold down the brakes and apply the parking brake (per the console) to reset (or do something) for the ABS..

 

Yes, I believe it will have to learn your driving style again. The custom timing, trims, etc. should be hard coded.

 

Battery out for that length of time is pretty much a reset.

Handy to know for those who get nervous about exactly how to to do it with the cables. Takes longer but works the same.

 

Not good to run an engine without a battery. Your alternator voltage regulator will be very unhappy about that.

 

Don't think he did that! He took the battery out of the Jag and used another car to take the battery around looking for a replacement.

 

Right, " in my Toyota" he said. That's good!

Battery life is highly variable. Generally speaking the number and depth of discharges is what determines battery life.

 

I recently sold my 04 XJ8. I did not drive it every day so I kept it on a Battery Tender when I was not using it. It still had the OEM battery in it!!!

 

Battery Tenders are the way to go for sure. My Corvette and VRod are each always on one and the XF is on one every weekend as I only drive it during the week usually.

Have never had a battery issue.