I have a 2008 xk. Just brought a new battery two weeks ago. Just drove the car three days ago. Now the battery is completely dead. Try to charge with a quick jump....the quick jump was drian in a matter of 15 seconds

 

Disconnect the battery and charge it up with a suitable charger (10Amp or greater). After it is fully charged remove the charger and wait for an hour or two and then check the battery voltage. If 12.6 V or better then hook it back up . Wait for an hour with the car shut and locked. Come back and check the battery voltage. It should be still around 12.6V. Start the car and read the battery voltage with engine at around 1500 rpm. It should read over 14 volts. Let us know.

 

"Brand new" batteries often sit on a retailer's shelf for months before they are sold. It's possible that your new battery was not fully charged when it was installed and wasn't driven far enough to recharge it.

If your XK is not your daily driver, I recommend that you buy a CTEK MUS4.3 battery maintainer (Amazon sells them) and use it every day. Always lock your car even when it's in your garage to shut down convenience mode and minimize battery drain. And keep the keys at least 20 feet away from the car so they don't wake it up.

It's also possible that your new battery is defective and needs to be returned for a replacement.