Replaced my batter with a Super Start Extreme from O'Reilly's... Not a bad price with the Memorial Day $20 coupon. ~$150 out the door after the core was returned (had a spare battery lying around that was toast as there is still some life in the Autocraft that came out of the X5). Specs at the link below.

Super Start Extreme 49EXT - Battery | O'Reilly Auto Parts

I only replaced the battery as a preventative measure. The one in the truck is from 2012 so not that old but I wanted a larger reserve capacity vs. the Autocraft one. I'll use the one I pulled out on my test bench for amps, wiring, etc.

Also replaced the bump stops for the rear tail gate with the newer designed spring loaded ones. Definitely worth the ~$38/ea the dealer charged me for them. Thanks again RB for the tip about the redesign/superseded part.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)