This is just an FYI from a personal experience. Don't be like me and not read the owner's manual section on a dead battery. I learned that the glove box will not open if the battery is dead and could not access the manual. Know how to unlock the trunk with the key that's hidden in the fob.

If you have an XF Supercharged your battery is the same size as the battery in a Ford F350 Super Duty. You cannot jump start these batteries with a portable jumper cable box. AAA tried to jump start mine that way, it failed, and they left. Luckily Jaguar Road Assistance showed up and knew the drill.

 

Yes, I hear that's a bit of a rigmarole in the new XFs. Very few portable booster packs will make much of an impression on a completely dead battery, never mind a large Jag battery or similar. But a Citroen Xsara at 2,000 RPM will! ;o)

 

One thing I learned about the portable battery jumpers is to hook them up and allow them to wait about 15 minutes and then start the car. Has worked for me every time.

 

Fyi, many inexpensive jumper boxes are pos's stay in the $150 and up, and yes the batteries in them go bad too but are replacable.

 

In addition, the AAA jumper box might have been on its 20th jump of the day. No jumper box will work if it is depleted or if it has corroded cables.

A fully charged jumper box with sufficient capacity and good cables would not be any different than a fresh battery.

 

That's a good practice with any charge source. It refreshes the dead battery a bit so that the start is not solely dependent on current flowing through iffy clamps. If the clamps are really bad but still passing current, it is possible to jump start from a running vehicle by letting the flat battery charge from the higher voltage available because the donor vehicle is running.

 

Never had to do this. Started dead cars in minus 35C with no delay at all. If the car battery is dead because it is not accepting a charge then waiting will just be hard on the donor car's alternator to no purpose. In that case one should start the car and drive it only to the battery replacement shop. Weak batteries kill voltage regulators quickly.

If the car battery is not dead but just insufficiently charged you won't need to wait. If the engine will crank it will start, eventually. Far more important than actual battery charge is the ability to crank for long enough to generate compression heat when starting a cold engine.