So im guessing its the battery?
 

Over the past few days Ive had to get a boost. the strange part about it is that the way it started dieing was if i parked the x for 24 hours and then i came back, I needed a boost. I went ahead and gave it one and then throughout the week it was fine, now about 2 weeks later it seems to be dying every time after i drive it.

Now, the only question I have is, simply where can i find the battery in the X? I know its somewhere under the rear seats? oh and of course which battery is the best to purchase? I here something called Exide but is there any specific model that best fits the X? Specifically for me since I have DEPO headlights and a bunch of crazy things that take a lot of battery life? or it shouldn't matter?

Thanks! Sim0n.

Dont pull up our seats just yet... the battery is under the spare wheel in the trunk!

Hey, thanks! Yeah i sorta figured that one out after researching a little more into it...

TKS, I just PM'd you, per your request, with a pic link and some helpful suggestions
for a DIY...
GL, mD

Simon, yes mine did the same exact thing before it fiinally completely died. You can get a new battery at any auto parts store and boom swap it out no problem.

Thank you so much for that awesome D.I.Y.

For those of you who have the same issue I have, check out this amazing D.I.Y. on how to change the batteries on our X's, by MotorDavid: EDU: How to change the battery in an X5 (2001 - ?) - bimmerfest - BMW Forums

I have to say I just changed my battery and it was very easy to do while following the D.I.Y.

Thank you very much MotorDavid :)

You are welcome, KingSim0n! Glad it went well. You are a patient
man reading my PMs to you, :D. More difficult to describe the DIY,
than it is to just show it. Hopefully, the XOutpost links get resurrected.
BR, mD

I had the same symptoms and bought a new battery from the dealer. ($144.99) Dead two days later. Turns out it was the final stage resistor drawing current from the battery when the car was off. The battery was probably due to be changed anyway since it was the original and it was going on 7years.