12.7 is fine with vehicle not running. 13.5v minimum with vehicle on, and since you have a 4.8is (any N62 really), running voltage should be ~14.3-14.5v

Not sure I'd focus on the battery. Did you disconnect the battery while working on the suspension? Not sure why you would have to, but thought I'd ask in case the cable was not tightened back up or something.

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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)