Help X5 dies then comes back to life after spark

[seanjohnnyc]

I am at wits end. I replaced the battery and Alternator six months ago. Car starts up fine after driving for an hour or so then i shut of the vehicle. After 2min tried to start the x again all of a sudden everything went blank from the navi to the radio. When i try to jump it by hooking up the plugs and accidently getting a spark without jumping it at all then all of a sudden everything turns on and able to crank up the engine again.

Is it a bad battery or is it the alternator?