I've always used battery tenders, especially on my motorcycles. They come with pigtails so I can leave connected to the battery post and just "plug it in" when done with a ride.

Depending on whether you need a tender or a charger on your X is dependent upon what kind of parasitic draw you have on the battery. My X5 has a 2 year old battery and never has been charged or tended, and the most I haven't driven it is like 2 weeks without starting and it's been fine, so it never needed it.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards