I guessed prices highly depend on location. Here are the So Cal prices:

Autozone = $140 + $12 core
Link => http://www.autozone.com/selectedZip,.../selectZip.htm

Kragen/O'Reilly/Advance Auto Parts/Partsamerica.com = $156 + $10 core
Link => http://shop.oreillyauto.com/ProductL...e=5005&PTSet=A

Interstate Batteries = $163
Link => http://www.interstatebatteries.com/c...818-4294493525

Sears doesn't show a battery for the X5, whether it's 3.0i, 4.4i, 4.6is, or 4.8is.

Crevier BMW (internet discount) = $220 + core

By the way...This is for the type 94 battery (for the 3.0i)

dkl - GREAT information!

Wow what a difference in batteries.

BMW's OE battery has 720 CCA and a 2 year warranty and runs over $200.
The Mega-Tron Plus seems to be the most robust and has 850 CCA, 1000 CA and an 85 month warranty and costs $163.
The Gold-Duralast has 760 CCA and an 8 year warranty for about $142.

Don't just compare CCA as most manufacturers would boast. Look and compare the Reserved Charge (RC) as well, which is often not published until you get the battery and read its label. For example, BMW's OE type 94 battery have an RC rating of 140. Autozone's Duralast and Batteries Plus' Werker have an RC rating of 130. Kragen/O'Reilly/Advance Auto Parts/Partsamerica.com's Autolite batteries, which is made by Exide, who also happens to make Sears' Diehard and Pep Boys' Bosch batteries all boast a very good CCA rating...way above BMW's OEM battery; but its RC rating is only 80 - almost half of OEM!

I try to avoid wringing hands over "close" specs...
the Werker I stuffed in my old '01 was 640 CCA and
130 RC; close enough esp. since I'm not running
boom boxes, parking it in Alaska, etc. My oem lasted
6 years and, if that replacement lasts 3-4 yrs, I will be
happy. Hope our '01 goes another 3-4 years, lol!

You are correct, but as you said that stat is rarely published. Do you happen to know what the best battery is for X5 cost no option?

Cost no option ?

I have a fairly audophile car stereo in mine, and I replaced with with a Odyssey Battery....1700MJT if I recall.

Are you certain it fit in the X5 trunk without any problems?

Pepboys $99 for the bosch 96 month. They also have the house brand.

Any idea how to do this oneself?

You'll need a battery load tester. Autozone used to provide this free service, but not sure if they still do. How old is your battery? I would just replace it if it's past 5 years.