I have 115K miles on my '01 and still have the original battery, so you should be fine.

I run my radio with amp all the time without the car on and have had no problems. I also keep a jump starter with me just in case

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2001 X5 3.0i (PP/WP/AP) Traded at 213K miles
RARE White on Black - Why does everyone get Tan??
First E53 with 215s on XOutpost!!