What are you planning to run on it? How many watts will you require, and is there a motor load, with any significant inrush current?

Small inverters just plug into the cigarette lighter, and would be simple to install. Larger ones (and perhaps even the smaller ones) could present a challenge for the electrical system in the X5.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue